Conception of the good

Insights into our current education system

Pt 2: Reattempting Circle Theorems

This blog post is a follow up of the ‘Reattempting Circle Theorems’ blog post series. Last time we looked at this circle theorem:

Circle Theorem #1: A right angle triangle in a semi-circle

We will now look at a potential non-circle theorem. I’m opening this up for debate. I’ve had a look around online and in articles whether ‘Two radii and a chord form an Isosceles triangle’ is considered a circle theorem or not. Right now, I’m going to state it is not a circle theorem but instead the start of a proof about the perpendicular bisector of a chord. Thank you to Ed Southall for clarifying. Follow him – he’s my geometry go to! I am flexible to change my mind.

I deliberately included this after the first circle theorem so I could interleave it into new problems.

If I have a triangle where two lengths are radii and the third length is a chord, then it will be an Isosceles triangle. Two radii connected by straight line at both endpoints form an Isosceles triangle. The two of the side lengths are of equal measure.

I hope all pupils will be able to access a mathematical problem like this:

Show that: Two radii and a chord form an Isosceles Triangle

Here is a diagram for you to see this circle theorem form:

I have a circle where I draw one radius:

I draw another radius:

I draw a straight line between the two endpoints of each radii which are on the circumference of the circle:

I then would show pupils that I can mark the two radii to show they are of equal length. I would show that the two equal angles of the triangle are of same size. And even mark the angles with identical values. I would do this live rather than with static images:

Now, there are two types of angles you can find:

1) One of the two equal angles

2) One non-equal angle

To find one of the equal angles, you’ll have the non-equal angle. Here are the steps:

  1. 180 degrees – non-equal angle
  2. Divide the result by 2

To find the non-equal angle, you’ll have one of the equal angles. Here are the steps:

  1. Double one of the equal angles
  2. 180 degrees – (double one of the equal angles) = Non-equal angle

The structure of the booklet is the same as outlined in the previous blog post. There are ‘I do, We do’ examples and then a practice exercise at the end. Since this isn’t a circle theorem, I’m not going to show a selection of examples and non-examples. But, I’m interleaving the first circle theorem into the sequence.

Finding the missing angle

Here are the teacher examples to find a missing angle or angles. The variation between the examples isn’t evident here. I try to change one thing at a time between the ‘I do’ and the ‘we do’ example. I’ll explain the thinking behind choosing each example:

1. Show that two radii and a chord form an Isosceles triangle, only. Given the non-equal angle, find the one of the two equal sized angles.

2. Show that two radii and a chord form an Isosceles triangle, only. Given one of the equal sized angles, find the missing non-equal angle.

3. Interleaving the angle fact: angles around a point sum to 360 degrees. Find the non-equal angle to then find one of the two equal sized angles.

4. Two Isosceles triangles sharing a length. One triangle you are given one of the two equal sized angles to find the non-equal angle. Once you’ve calculated ‘m’ you can use the basic angle fact that angles on a straight-line sum to 180o to find ‘p’.

5. Same as Example 4 – angles needed to find before ‘u’ are not marked. Same logical steps. Also, can use the fact that angles on a straight-line sum to 180 degrees to then find ‘u’.

6. Interleaving the first circle theorem – A right angle triangle in a semi-circle

  1. Identify ‘a’ as a right angle of 90 degrees.
  2. Find ‘e’ by adding 48 and 90 degrees and then subtracting from 180 degrees.
  3. Find ‘b’ by finding the non-equal angle of the triangle using 180 – 58 degrees, and dividing the result by 2

7. Three Isosceles triangles.

  1. Find ‘m’ and ‘n’ by doubling one of the two equal sized angles of each triangle and subtracting from 180 degrees.
  2. Find ‘k’ by using the fact that angles around a point sum to 360 degrees.
  3. Use ‘k’ to find angle ‘p’ by subtracting the non-equal angle and dividing the result by 2.

8. Two Isosceles triangles that are not sharing a side length:

  1. Find ‘u’ using the one of the two equal angles of the triangle
  2. Find ‘w’ by doubling the triangle’s two equal angles and subtracting from 180 degrees.
  3. Find ‘x’ by doubling 64 degrees and subtracting from 180 degrees.
  4. Find ‘y’ by using the angle fact that angles around a point sum to 360 degrees.
Algebraic Application

Another reason why I wanted to include this feature because it allows pupils to apply prior knowledge from the topic of solving equations. There are two problem types that we will have to deal with:

  • Two equal angles labelled – solve equations with unknowns on both sides

In this case, the variable used for the two equal angles represented as expression will be the same. It has to so we can form an equation with unknowns on both sides to find the value of the unknown. I then labelled the non-equal angle with a different variable. I did this because I didn’t want to make an error in choosing an algebraic expression which shared the same variable as the two equal sized angles.

  • All angles are an algebraic term, expression (same variable, not different) or number. Form equation and equate to 180 degrees

In the next problem type, I deliberately labelled the two equal sized angles with the same algebraic term or expression. This re-iterated that the two angles of the Isosceles triangle are equal. Given more time I would create more examples where the equal sized angles are labelled with different expressions sharing the same variable.

Is it possible for a mathematical problem be incorrect?

Thankfully, Tom Francome highlighted that I mislabelled one angle in a triangle with a different variable so the possibilities for that variable were endless:

I changed ‘4c’ to ‘4f’ so that all angles in this triangle share the same variable. We can then collect the algebraic terms and equate to 180o to find the value of the unknown. We can substitute the value of the unknown back into the algebraic term to find the size of each angle.

Booklet attached:


Reattempting Circle Theorems

In January 2017, I wrote two blog posts on a selection of circle theorem resources. I was in my fourth year of teaching and I loved creating curriculum resources. I made the problems using activinspire because I hadn’t mastered Geogebra by that point. There were so many mistakes in the questions.

Some lovely teachers got in touch via DM and gave their friendly feedback. Others wielded their axe and punched me with mean tweets. Some others pretended to care by writing blog posts about the situation. As if they knew the cause behind my errors.

It wasn’t the best of times. But, I learnt that it is OK to make mistakes that you didn’t even know were mistakes. It highlighted that subject knowledge development is never ending.

What have I learnt from the experience:

  1. Using GeoGebra meant that I was able to draw the angles, so a 26 degrees angle looked like one. The largest angle was opposite the longest side length etc.
  2. I was able to check that all the angles within a triangle and a straight line totalled to 180s. And that angles in a quadrilateral or around a point totalled to 360 degrees.
  3. I was able to learn about construction invariance – something I didn’t know about. It is also something taught after A level Mathematics. My knowledge of school taught mathematics goes this far.
  4. Always have your work reviewed by a fresh pair of eyes. Ask a friend, a colleague etc.

I am familiar with Geogebra and enjoy using the application. Last year I re-created the circle theorem resources into a prepared booklet. I will release each circle theorem’s resources one blog post at a time.

Here are a few things to know about the resources that you are about to see:

  1. The first section is showing pupils how the circle theorem comes into existence. Starting with the circle and outlining its features to deduce the circle theorem. If I showed this in class, then I would do this live rather than using static images.
  2. I then show a series of examples and non-examples of the circle theorem. This helps pupils to identify a circle theorem on complicated problems.
  3. I start with examples which model the circle theorem in insolation. So, a pupil’s attention is on the theorem alone and identifying the missing angle.
  4. I then start interleaving basic angle facts in the circle theorem problems. E.g: angles in a triangle, straight line, right angle, isosceles triangle etc.
  5. In future circle theorem resources, you will see me interleave learnt circle theorems. This is to build gradual difficulty within the examples.
  6. There is algebraic section included at the end where angles are expressions.

One common question I get from the resources I make: which sets are the resources appropriate for?

My answer: all sets!

This isn’t a popular answer but it’s true. When you are teaching a concept for the first time the teaching should be the same for all sets. The only difference between high and low attaining pupils is the time taken to learn the concept. High attaining pupils recall prior knowledge and using it with fidelity compared to weaker pupils. I would teach a new concept explicitly with all pupils across the attainment spectrum. Can you imagine your low-attaining pupils finding the missing angles on this problem?

Introducing the Circle Theorem: A right angle triangle in a semi-circle

Here is a circle:


Draw a line from one point on the circumference, through the centre of the circle marked ‘C’ through to the opposite end on the circumference. This line is the diameter:

Teacher Language: Edge – Centre – Edge – check it is a straight line!

Draw a straight line to another spot on the circumference in one half of the circle from one end of the diameter:

Complete the three-sided shape (triangle) by drawing a straight line between the two unconnected points:

We have a triangle that is within a circle, and all the triangle’s vertices are on the edge of the circle. In other words, all the triangle’s vertices are on the circumference on the circle. The angle on the circumference, not touching the diameter is 90 degrees. It is a right angle. This is a right-angle triangle.

Introducing Examples and Non-Examples

Specify the language to state the correct circle theorem example and its non-example.

For example:

“If we have the longest side of the triangle as the diameter of the circle, then we have a right-angled triangle.”

For a non-example:

“If the longest side of the triangle is NOT the diameter of the circle, then we don’t have a right-angled triangle.”

The right angle is always touching the circumference! ‘a’ in the examples mark the right angle:

Finding the missing angle using the circle theorem

At this point, I would state the steps to find the missing angle before looking at a few examples.  Pupils can follow the steps if they lose track during the example explanation.

Here are the steps:

  1. Identify the right angle of the triangle
  2. Calculate the remaining interior angles by
  3. Adding the known angles
  4. Subtracting the result from 180 degrees

I usually do a ‘I do, We do’ set up when going through teacher examples. I will go through one example, and then pupils will go through a similar example. Same problem just different numbers. Completed on mini-whiteboards. Here is an example:

Example 1: Find the missing angles:

Here is the teacher sequence series only (‘I do’ only):

Example Breakdown:

  1. Circle theorem in Isolation – Find right angle and second missing angle
  2. Circle theorem in Isolation – Find right angle and second missing angle
  3. Interleave an Isosceles right-angled triangle
  4. Find the missing angles across two right-angle triangles. One being an Isosceles triangle.
  5. Same as example 4 but both triangles are in the same semi-circle
  6. Interleaving angles on a straight line

I included Example 5 to relate to a future circle theorem: Angles in the same segment are equal.

The algebraic section is incomplete. I thought I’d include it to see the variation theory applied in the examples.



Varying Surface, Varying Depth

A month ago, I was resourcing for the topic ‘Expressions and Substitution’ for the Y9 Curriculum. A common approach is to substitute values to then solve a linear equation. I was keen to create a problem type when you substitute values you then have to solve a quadratic equation. Something like this:

On the surface you can see that the sequence of examples have one aspect varied at a time – value for ‘u’. This is inspired from Ference Marton’s Variation Theory (VT). One theory out of a body of educational research underpinning the United Learning Mathematics resources.

We use VT because perceived variation generates expectations for pupils. When these expectations are confirmed pupils’ perceptions are relevant mathematically. VT guarantees more clarity and honesty about mathematical ideas. Anne Watson and John Mason explain the meaning of ‘clarity of mathematical ideas’:

“the structure of examples through which learners encounter mathematically significant variation…attention can be focused on the use of variation to reveal the patterns and generalities which result from the techniques. This is the clarity.” ¹

This blog post will look at how VT is applied on the surface by changing the value of ‘u’, but also resulting in one change in the procedure of factorising a quadratic expression. This post is about the thinking behind creating an exercise like this, teaching it would be different post. To appreciate what follows here is the working out for part (a) and part (b)

On the surface, you can see that only initial velocity’s value changes. This is deliberate. Under the surface, here are the quadratic equations for each part to show that only one thing is changing between each part:

Pupils overgeneralise the procedure of substituting values to then solve a quadratic equation.

This example shows variation on the surface, but also with the quadratic equations solved so pupils develop mathematically relevant expectations that they will be solving a quadratic equation.

Here is the thinking process behind making this exercise:

Step 1:The kinematic equation where t is unknown results in solving a quadratic equation:

Step 2: I then thought what would have to be the unknown variable and the known variables? For the following formula to result in a quadratic equation t is unknown.

Step 3: In Y9, pupils can factorise a quadratic expression where all coefficients and constants are integers, and where the coefficient of ‘a’ in a quadratic equation of ax² + bx + c is equal to 1, only, not greater than or less than 1.

I have to be selective with each known variables’ values. Some are permissible and where some aren’t. The values that aren’t permissible would mean pupils factorising a quadratic expression where ‘a’ in ax² + bx + c is greater than 1.

Step 4: I looked at a sequence of quadratic expressions that can be factorised. Variable t will be the unknown rather than x to correspond to the kinematics equation:

So, here is the sequence I made:

There are a few expressions that I can’t factorise because of the context of the kinematics. During the solving process, I can’t have two values of  t being equal to a negative value. I can’t have this situation below:

In the context of kinematics, I can’t have negative values for time. Deciding which one to pick will confuse pupils.

I can have either: a quadratic expression where t would be both positive, or one value of  would be positive and the other negative. If there are two positive values for time, then that means the case is true at two different times. If one value of time is positive and the other is negative, then we accept the positive value for time only. In sum:

I can’t have a quadratic expression where the constant is positive AND the value of ‘b’ in ax² + bx + c is also positive.

I can have a quadratic expression where the constant is negative AND the value of ‘b’ in ax² + bx + c is either positive or negative.

Step 5: Back to the condition stated in Step 3 where the coefficient of ‘a’ in a quadratic expression of ax² + bx + c is equal to 1, only.

For this to be the case, I know that

The value of ‘a’ cannot vary, because pupils will have to factorise a quadratic expression where ‘a’ in ax² + bx + c is greater than 1.

Step 6: If we look back at the sequence of quadratic expressions, I have kept the value of the constant the same -24. And since,

The value of ‘a’ and ‘s’ remain the same throughout so the only varying value is for ‘u’ . Initial velocity can be positive or negative because it is a vector quantity.

In summary, on the surface of the exercise only the value of initial velocity varies at a time. Beneath the surface, one coefficient of the quadratic expression varies at a time. We are varying on the surface and deep within the mathematical problem. The two controlled dimensions encourages the learner to find the value of t:

  • By overgeneralising the process of substituting to then solve a quadratic equation.

Pupils focus on this overgeneralisation because they can factorise the quadratic expressions used. They learn the mathematical structure to substitute and solve a quadratic equation.

  1. References:

¹ Anne Waton and John Mason (2006) Variation and Mathematical Structure MT194

This exercise is under review. If you spot an error or have any feedback then please feel free to get in touch. 

Engelmann: Communicating through Covertization

Chapter 21, in Engelmann’s Magnus Opus, Theory of Instruction has changed the way I sequence worked examples to communicate a concept. This change took place greatly whilst I was at Michaela Community School when I started experimenting how to teach a UK Maths Challenge After school club. This is written about in more detail, here.

What I noticed, which may sound obvious, is that if you teach using examples which demonstrate the explicit features of a concept first and then progressively make those features implicit then the probability of success for each child in the learning process is greater. Engelmann refers to this as Covertization, “instruction that involves prompt shifts progressively from highly-prompted examples to unprompted examples.”

One example which will be detailed below, would look like this:

So a sequence of examples with explicit features transitioning to implicit features provides a process where pupils take overt steps to go from the first line of working to the last line of working. This means that the first example pupils encounter is structured within the simplest context.

Covertization results in examples that communicate a concept, or part of a concept, to be communicated in its most explicit and misconception-proof form.

The best way to appreciate covertization is to look at some examples which aren’t explicit.

Here are examples of fractions:

Here pupils can develop the following misconceptions:

  • all fractions have a one at the top
  • all fractions increase by ‘1’ in the bottom value
  • fractions get bigger when the bottom value is greater

Another example:

Here are examples of expressions commonly known as a ‘difference of two squares’

Here pupils can develop the following misconceptions:

  • The first term is always positive and a
  • The second term is always a constant
  • The second term is always an integer
  • The second term is always negative

What are the examples that I would use instead? To communicate an expression as a ‘difference of two squares’ I would start with the following, by stating that an expression must meet the following conditions:

  1. The coefficient of the variable is a square number
  2. The power of the variable must be even
  3. The power of the variable is never an odd number
  4. One term will be negative AND the other term will be positive
  5. The constant must be a value that can be square rooted.

Here are the following examples that I would use to reiterate the conditions stated above:

There are other examples that I could include here, however, what I’ve done is limit the examples to only meet the conditions I’ve stated. But look at the complexity of what pupils can identify as an expression known as a difference of two squares by selecting the examples that I have.

More importantly, I’ve started with an example which is explicit with the features that make an expression a difference of two squares. With the initial set of examples, you can see that the coefficient of 1 for isn’t obvious because pupils can’t see it, and ‘1’ as a constant isn’t an obvious example of a square number. Explicit features allow pupils to build a clear and misconception proof understanding of a concept, which is what makes an example powerful.

My final point, we can see that the process of covertization has highly prompted examples allowing pupils to respond successfully to writing the product of two expressions because the coefficients and powers provide them that structure. Starting the other way around with implicit features now looks unstructured and poorly guided for a pupil to know how to rewrite the expression as a product of two expressions.


Thank you, Siegfried Engelmann. Thank you.

On February 15th, the world lost an educator who spent his life developing an approach to accelerate the learning of disadvantaged pupils.

Engelmann was a Marketing Director turned Professor Emeritus of Education at the University of Oregon. He co-authored the famous ‘Theory of Instruction’ with Douglas Carnine and co-developed the term ‘Direct Instruction’ while working with Carl Bereiter. Through grant funding, they set up the Bereiter-Engelmann Pre-school which demonstrated the extent to which disadvantaged pupils could accelerate their learning in comparison to the performance of middle-class pupils.

I have spent the last couple of years becoming familiar with Engelmann’s work, taking aspects of his Theory of Instruction and applying it in my resource creation.

So, what have I learnt from Engelmann?

Answer: That a learner’s inability to respond appropriately to a form of instruction may not be the fault of the child; instead, it can be a problem with what she’s being taught.

This means it’s possible to teach a syllabus in a way she can respond to appropriately without dumbing it down. Here are the four things I keep in mind when creating resources that allow the highest percentage of pupils to understand the course content on the first attempt.


When I used Engelmann’s Connecting Maths Concept textbook series with my Year 7 and Year 8 Intervention pupils, I saw that Engelmann had taken a concept and broken it down into several sub-tasks. A sub-task is a small aspect of a concept. For example, A sub-task of how to add fractions with denominators would be finding the lowest common denominator. For a pupil to develop a flexible understanding of a concept, she needs to be taught as many sub-tasks of the concept and then shown the connections between each of the sub-tasks.

Atomising does exactly this. When I plan a unit of work, I take a concept and break it down into its sub-tasks, and I explicitly teach even the most nuanced aspects of the concept. For example, before I teach pupils how to factorise an expression, I teach pupils how to divide an algebraic expression by an integer, or by an algebraic term. Before I even do this, I teach pupils whether we can also divide an algebraic expression by a number or an algebraic term. An example is shown below:

Here are some examples, of where we can simplify the algebraic fraction:

Here are some examples of where we CANNOT simplify the algebraic fractions because we cannot divide ALL the terms in the fraction:

The value of this exercise is two-fold:

1)      Pupils are taught the most nuanced aspects of a concept which are usually the most difficult parts of the unit being taught. If the most challenging part of the concept isn’t taught explicitly then how can we expect pupils to attempt the most complex applications of the concept? We need to be more thorough and comprehensive than you might think and teach the most complex elements of a concept as well as the most basic.

2)      Pupils develop a flexible understanding of the concept because they can see the big picture. If you plan an entire unit rather than isolated lessons parts, you are more likely to teach as many sub-tasks as possible and not miss anything that’s essential to a student’s understanding. Missing out sub-tasks inevitably means you have to re-teach. Engelmann set up his textbook series to avoid the need to re-teach. If re-teaching is required, Engelmann provides appropriate correction and reinforcement exercises for each unit of work.

Sequencing the learning in the most effective manner

Engelmann’s Connecting Maths Concept textbook structures the content of a unit of work in just that sequence where the learning can be delivered most effectively. Engelmann believed that all future learning is dependent on prior learning and that there is an optimal sequence for each concept. Provided the lessons are sequenced in the most effective way, pupils always have the knowledge required to access the topic they are about to learn. At United Learning, scheme of work is structured and resourced with the same philosophy in mind. The underlying idea is that how effectively the pupils learn depends on the sequence in which they learn about a particular concept.

Scripting the lessons – Pedagogy

Scripting how you communicate the concept is essential. Now, many teachers despise scripted lessons, and some with good reason, e.g. the script they’re expected to follow is sub-optimal. Another reason for their scepticism is the belief that there is more than one optimal way to teach pupils about a particular concept. However, Engelman persuasively argues that there is only one optimal way to teach a particular concept – and his scripted lessons were field tested with tens of thousands of pupils and constantly being refined in response to feedback. Consequently, he was confident that the scripted lessons he and his colleagues developed embodied the most optimal learning sequences.

When I created my resources at Great Yarmouth Charter Academy, I started scripting how I would communicate concepts, to ensure pupils received the most effective and efficient form of instruction.

Then, I would think carefully about what method to communicate.  For example, I didn’t want to teach pupils how to add fractions using a method which was limited to only a few problem types, and then create a different method for another set of problem types. Instead, I tried to create methods that could be applied consistently to as many problem types as possible. This allowed pupils, especially the weakest, to master each concept in all its myriad complexity; evidenced by ever increasing scores in weekly quizzes.

Lastly, my scripted lessons were designed to give pupils the grounding they needed to articulate their understanding. Here is a video showing how a pupil using this knowledge to subtract negative fractions:

Low-stake quizzing and providing appropriate corrections and reinforcements

Engelmann’s Connecting Maths Concept textbook has many opportunities for pupils’ understanding to be tested. The script includes hundreds of questions for teachers to ask. Pupils are given exercises to try with the teacher, as well as independent exercises. Similarly, after every ten lessons, there are also small quizzes recapping what pupils have learnt, not only in the last ten lessons but in the previous 20, even 30.

At Charter, one visitor tallied the number of questions I asked pupils in a single lesson, and they totted up 76 questions in about 25 minutes. I learnt from Engelmann’s teacher scripts how to ask pupils’ questions which test their ability to recall prior knowledge, articulate their knowledge of a concept, to explain a misconception, etc.

In summary, I believe that Engelmann is one of the most important educators of the 20th and 21st Century. I think his work will stand the test of time. By applying his teaching principles to resource creation, I have helped my pupils learn more, and remember it for years to come.  My experience confirms, for me, that teacher quality is a function of the resources they have access toChildren are more likely to be successful with a teacher, who has access to exceptional resources, than a teacher who doesn’t, and never has.

Engelmann’s work has taught me more than any educator that I studied with during my PGCE and MA. My next post will look into the evidence for the effectiveness of Engelmann’s approach and the reasons why his work hasn’t been more influential.

After my podcast with Craig Barton, I have received many emails asking to share more booklets. I have attached the booklets that I made during my time at Charter. They aren’t perfect, and with my current workload, I am not in a position to refine them. However, I do think they are useful for teachers who want to start designing their own booklets. I used each booklet with all my classes. I hope they are helpful.

There will inevitably be mistakes in the booklets. I take full responsibility for any errors that you see.



Teaching an Inquiry Maths Problem

In February 2018, I heard Andrew Blair speak at a CPD event about Inquiry Maths. Andrew is a Head of Maths and founder of his website Inquiry Maths where teachers can gain access to ideas about teaching Mathematics using the Inquiry Maths model.

Andrew and I tend to disagree over the best pedagogical approach when teaching Mathematics, but we agree in teaching many of the problems that he has shared on his website. When I create resources, I check out different sites for ideas, and I regularly check Andrew’s website. It’s fantastic! When I saw Andrew speak at this CPD event, he showed a mathematical inquiry task that I made a mental note to include in my resourcing for the following year. The problem is below:

40% of 70=____% of _____

I love this type of mathematical problem. There is so much mathematics that needs to be communicated, and I would recommend readers to check out Andrew’s page on this inquiry. At United Learning I’ve finished the Fraction, Decimals and Percentage booklet for the Y8 curriculum and I’ve made resources for this type of mathematical inquiry to be shared with the kids.

Here is an example of how I broke down the teaching sequence so all pupils can access a problem like this but also support all pupils to attempt more complex forms as well. 

The teaching sequence is designed to increase the probability that all pupils can be successful in learning the subject content. 

1) Showed a multiplication model for the following problem types

I have listed some of the potential decimal multiplication calculations and then demonstrated how to draw the model for the equivalent decimal multiplication calculation:

Pupils are only shown the first line because they are taught that the mathematical model of rewriting the decimal multiplication calculation.

A few points: I’ve deliberately kept the position of the mixed number or decimal and the integer in the same place within the calculation. In the second example, the first term of the calculation is a mixed number and the second is an integer, it is the same on the right-hand side of the equal sign. This is because I want pupils to focus on the digits changing position, and that only. Everything else is kept constant.

This is how I would communicate the model in the classroom to pupils:

I am multiplying a two decimal places decimal by an integer, so my equivalent calculation will have a two decimal places decimal and an integer.

I would get kids to draw the underlines to show me how their equivalent calculation would look. I have done this because learning the mathematical structure of the calculation is another thing a pupil needs to learn. This also reduces the likelihood of a future error caused by pupils by not knowing whether the calculation will have an integer and a decimal, or an integer or a decimal, and how many decimal places the decimal will have.

2) Introduce the steps to go from the problem to the equivalent calculation

a) Rewrite decimal place structure
b) Fill in the digits from the right side
c) CHECK: Multiply out both sides of the calculation to see that the result is the same

In my teaching, I write the generalised steps for the calculation pupils are about to do because they can see that even if I am rewriting a multiplication calculation with

  • an integer and decimal or;
  • two decimals or;
  • decimals with the same number of decimal places or;
  • decimals with a different number of decimal places

the generalised steps remain the same.

Generalising method stops is something that Siegfried Engelmann calls ‘Logically Faultless Communication’ which has been blogged about here.

A logistical thing, it also allows pupils to follow the steps better if they can flicker their eyes from the live worked example demonstrated by the teacher and the steps already written on the board.

3) Introduce the Example-Pupil attempt sequence

At this point, I then design the teacher-led worked examples and the pupil attempt questions. The problem type that the teacher goes through and the pupil goes through after seeing the teacher demonstrate the same problem type.

Here is the sequence:

Pupils aren’t evaluating the calculation. They are rewriting the calculation so their answers would look like this:

I have deliberately started with explicit examples meaning that the 2 decimal places decimal and two-digit integer have digits more than 0. Only from example 4, I have introduced a single figure of 5; this is because pupils must write the digit 5 as 0.05 where there is a zero between the decimal point and the 5. Starting with explicit features such as digits more than 0 in decimals and integers makes the change from one calculation to the equivalent one more clear.

Pupils then will complete a practice exercise where they will rewrite a decimal calculation but ending in the same result as the first decimal calculation.

They will then transition onto a filling in the blank exercise like shown below:

4) Equating Percentages: Introduce the Example-Pupil attempt sequence

I believe that I’ve now taught all the prior knowledge pupils need to complete this statement:

40% of 70=____% of _____

The prior knowledge is listed below:

  • Writing a percentage in its equivalent decimal form
  • Rewriting a decimal multiplication calculation in a visually different form but where the result is the same as the original calculation
  • Decimal place value
  • Evaluating decimal multiplication calculations

Given that the prior knowledge has been taught and committed to long term memory, there is only one new thing pupils need to learn to complete the statement. They need to write the percentage as a decimal and replace the ‘of’ with a multiplication sign. Then every other line of working is prior knowledge that has already been covered.

Here is the working out, and the new line of working is in bold:

40% of 70 = ____% of _____
0.40 × 70 = __.__ __×____
0.40 × 70 = 0.70 × 4

5) Comparing Percentage Increase/Decrease

What has been learnt here can also be used to complete statements like this below, and place the correct symbol between the statements <, > or =

6) Equating Percentage Increase/Decrease

The next level of difficulty that is accessible because of the prior knowledge taught is that pupils can evaluate the complete statement and equate the result to the incomplete statement.

Here the new knowledge being taught is dividing the result by the value in the incomplete percentage calculation.

However, what makes this more complex is that you must evaluate the complete calculation and equate the result to the incomplete calculation to then find the missing percentage. So pupils must:

1) Convert the decimal into a percentage
2) If the calculation is a percentage decrease, then subtract the percentage from 100%
3) If the calculation in a percentage increase, then subtract the percentage from 100%


I appreciate all the beautiful problems and mathematical tasks that Andrew provides on his website. They are incredibly rich in knowledge and can create a valuable mathematical conversation between teachers and pupils. There is a great deal of importance in teaching inquiry tasks because it is an opportunity to develop a flexible understanding of the subject. However, where I would disagree with the Inquiry Maths model would be how the mathematical task would be used and how the content would be taught to children. I think there is a great deal of prior knowledge that needs to be sequenced, so all future learning is supported by prior learning, and that only one new thing is being taught at each part of the sequence. This is to avoid cognitive overload.

I hesitate to have pupils taking responsibility for directing the lesson because each child will focus on a different aspect of the mathematical problem in front of them. More importantly, they will focus on various aspects depending on what knowledge they already have. It is inevitable that in any learning experience, each pupil will be starting at a different point based upon how much knowledge they have. However, when pupils direct the lesson that will result in more knowledgeable peers leading the lesson, and weaker pupils struggling to identify or learn aspects of mathematics that they need even to attempt the mathematical problem. By laying out the prior knowledge and sequencing it, you are allowing the more knowledgeable pupils to consolidate any existing knowledge they may already have, but you are letting the weaker pupils close any gaps they may have. Overlearning is an essential part of the learning process; it helps the more knowledgeable pupils to learn something to the point that they never make a mistake.

This attempt, I believe allows all pupils regardless of their knowledge gaps to have any missing gaps filled, but also allows all pupils to be able to access the mathematical problem.

#Mathsconf18: Atomisation Pt 2


 #Mathsconf18: Atomisation Pt 2

Atomisation: Breaking down your teaching as you have never seen before…

On Saturday 9th March I delivered a workshop at the La Salle Mathematics Conference in Bristol. This blog post is a summary of some of the points made in the session.

For this workshop, I chose to look at an uncontroversial topic such as Angles on parallel lines. I think it’s uncontroversial because teachers know that it is an undeniable part of geometry that is commonly assessed. Also, I think it’s a topic which is taught with a poor sequence of examples. Lots of angle problems on parallel lines feels like an angle chase – when you find one angle then how can you find the other angle. However, in the process, pupils can’t have the rich mathematical discussion between the relationships of different angle facts on parallel lines. Part of teaching this topic effectively is dependent on the sequence in which the examples are organised.

When I started making the worked examples for this topic, I thought about the simplest application of angles on parallel lines for each angle fact and the most complex application. What I realised is that I could have spent hours or even days making lots of different worked examples. To avoid this, I thought of how I could cover all the myriad of complexities for each angle fact within the fewest number of worked examples.

The first step was to write out all the sub-tasks that I planned to teach:

–   Vertically Opposite Angles are Equal

–   Alternate Angles are Equal

–   Co-interior Angles sum to 180o

–   Corresponding Angles are Equal

–   Basic Angle facts on parallel lines

–   Angles on parallel lines – Algebraic

o   Simplified expressions equal to 180o or 360o

o   Simplified expressions equal to form an equation with unknowns on both sides.

After I listed the sub-tasks, I realised that I wanted to try a different pedagogical approach from the status quo approach. Historically, pupils are told that one unknown and one known are equal, and they are to accept it, and then identify the unknown and known angle pair which are equal in a similar looking example. Instead, I showed a selection of worked examples where the angles were of equal size, and I would state that these two angles are equal. I used Geogebra which is an online graphing programme where I would have an interactive set up so if I moved one of the parallel lines or the traversing line, the equal-sized angles would change from what they were before, but they would still be equal.

So, using a sequence of worked examples, I would

1)   Show the relationship with the position of angles and the angle fact

2)   Find the missing angle

3)   Find the missing angle by using a basic angle fact

NOTE: Diagrams aren’t drawn to scale here.

Vertically Opposite Angles are equal

Here is an example sequence for Vertically Opposite angles being equal

Show the Relationship

At this point, I transitioned to asking pupils in a whole class discussion the size of the unknown angles because they had seen the relationship between the position of two vertically opposite angles.

I deliberately used more challenging examples for pupils to identify one missing angle which is vertically opposite to one known angle. This is because I knew it is these type of angle problems, they would struggle with the most so I went through it with them so they would be successful when they would attempt similar issues independently. I felt that showing the relationship was explicit enough for pupils to attempt the simplest applications of identifying vertically opposite angles being equal.

The third section is using basic angle facts from the list below:

  1. Angles in a triangle sum to 180o
  2. Angles in a quadrilateral sum to 360o
  3. Angles on a straight-line sum to 180o
  4. Angles around a point sum to 360o

To either use the angle fact to determine one of the two vertically opposite angles or find one of the vertically opposite angles to then find another angle using one of the basic angle facts.

Here are some worked examples of this with an explanation:

I made Example 4 deliberately to highlight that the small triangle FCB and the large triangle KCE have the same angles.

In Example 5 and 6 I have included 2 parallel lines and 1 parallel line segment to allow Example 5 to include an opportunity to use the ‘Angles around a point sum to 360o’ fact. Similarly, in Example 6 I deliberately didn’t label the vertically opposite angle because I want pupils to start finding angles that aren’t labelled but are required to find another unknown angle.

In summary, I followed the sequence structure of:

  1. Show the relationship
  2. Find the missing angle using the angle fact given
  3. Find the missing angle fact using basic angle facts to then determine angles using the new angle facts learnt.

Alternate Angles are equal

Here is a worked example sequence showing the relationship in positioning of Alternate Angles being equal

Now using the same geometric structure as the worked examples used to show the relationship of alternate angles, I’m asking pupils to find the size of the missing angle:

Here is a sequence of worked examples where basic angle facts have been interleaved:

Co – Interior Angles sum to 180o

Here is a worked example sequence for Co-interior angles summing to 180o

In Example 7 and 8, pupils can see that each triangle formed by both traversing lines and one of the parallel lines all have the same size angles.

Here are examples where pupils are asked to use the fact that co-interior angles sum to 180o to find the missing angle:


In the last two examples we can explore so many interesting mathematical patterns between co-interior angles and parallel lines. In Example 6, A = I and G = C

Here is the next section of worked examples where basic angle facts are being interleaved:

Corresponding Angles are Equal

Here is a worked example sequence for Corresponding angles being equal

Here is a worked example sequence where pupils are using the angle fact that corresponding angles are equal to find the missing angle:


Here is a worked examples sequence where basic angle facts are being interleaved with the angle fact that corresponding angles are equal:


#Mathsconf18: Atomisation Pt 1

Atomisation: Breaking down your teaching as you have never seen before…

On Saturday 9th March I delivered a workshop at the La Salle Mathematics Conference in Bristol. This blog post is a summary of some of the points made in the session.

This presentation was on the topic of atomisation. Recently, atomisation has created a lot of conversation on Twitter and at a couple of conferences. What is atomisation and is it the next fad?

It’s not the next fad.

Atomisation is the process of breaking down a topic into its sub-tasks.

Atomisation is a term coined by Bruno Reddy who taught me about it during my second school placement in 2014.

Atomisation is the starting point to every booklet I create in my role as Curriculum Advisor at United Learning. I sit down and list all the sub-tasks that I need to teach that is within the topic. An example of this for Perimeter is available here.

What are the benefits of Atomisation in respect to the big picture?

Atomisation is a process in which teachers can collaboratively identify the specific and detailed knowledge that pupils must know to be academically successful.

Identifying this specific knowledge means that pupils can learn as close to 100% of the domain of knowledge that they need to know. Exam boards and the national curriculum, truthfully, may provide high-level specificity of what needs to be taught, but not the finer details or detailed knowledge that goes into making pupils able to do a task.

For example, pupils are expected to know the following fact below:

Fraction x Fraction’s Reciprocal = 1

And upon reflection, this seems understandable in respect to multiplying fractions, index notation, ratio, proportion etc. but it is not necessarily explicitly stated in exam board specifications or Curricula.

The lack of detailed knowledge outlined by exam boards or textbooks results in teachers reducing the subject content being taught. And the source of information of what needs to be taught from children usually comes from exam tasks, and then the curriculum becomes an endless repetition of exam materials. Similar thoughts have been shared on Daisy Christodoulou’s blog.

Mathematics as a subject is vast. There is so much to teach a child in the space of their academic career. Here is a visual:

If the bubble represents 100% of the domain of knowledge that needs to be taught. It is the case that we teach small samples of that domain. We teach concepts and how they overlap with other concepts, and we also teach connections between different concepts. However, if we use exam boards and textbooks as our source of information of what needs to be taught in the curriculum, then we inevitably miss out teaching other parts of the domain.

The process of atomisation enables teachers to focus on the concept and identify the finer details that aren’t readily available. Atomisation allows the teacher to teach as close to 100% of the domain of knowledge.

What are the benefits of Atomisation in respect to the teaching process?

Identifying and sequencing all the sub-tasks and specific knowledge that needs to be taught for a concept increases the probability each child will be successful in the learning process.

This means that pupils will be able to appropriately and accurately respond to planned questions, or that they will remember what has been taught at that moment after a long period.

Teaching aspects of a concept that are usually overlooked undermine how successful each pupil will be in respect to their future learning.

For example, not teaching pupils that:

Fraction x Fraction’s reciprocal = 1

undermines a child’s ability to attempt questions like this:

Show that the ratio in the form 1:n can be written as 1: 1.5

If pupils get these questions wrong, then the incorrect inference is made. Instead, they must be retaught the topics of ratios from the beginning, but they only need to be taught this fact. And this is a fact has been mentioned several times in the Year 8 Curriculum so far. I’ve resourced a section on problem types like this for the most recent ratio booklet coming out.

Teaching all the sub-tasks of a concept and sequencing it in a logical sequence prevents pupils from being cognitively overloaded because each sub-task taught is being used or covered in future learning. In the teaching process, pupils will have committed prior knowledge in their long term memory so any future learning will occupy space in their limited working memory.

What are the costs of Atomisation?

The cost of atomisation is a valid one. The initial stages of teaching a concept take more time to cover the content. If we explicitly teach more sub-tasks than we would normally then we would have more time available to teach the rest of the curriculum. However, by not explicitly teaching all the sub-tasks of a concept it will result in the following consequences:

  1. Reduce the probability of a child learning parts of a concept on the first attempt
  2. Undermine a child’s ability to access future learning

Atomisation avoids these inadvertent consequences by:

  1. Guaranteeing a greater likelihood a pupil will learn the sub-task on the first attempt
  2. Increasing the probability of success when learning future content or more complex applications of the concept
  3. Saving time in the future which would be inevitably spent re-teaching
  4. Revealing sub-tasks that need to be taught that are usually overlooked in the curriculum.

In summary, Atomisation has improved my teaching and as a result my pupils learning more and remembering it a half term later, a year later etc. More importantly, it benefits the children that struggle with learning the most. Atomisation has allowed my weakest pupils learn more in less time, and in my small world, I believe that this is a path that I will continue down when creating resources.




Reflections of 2018 Pt1: Great Yarmouth Charter Academy: Pinnacle of Teaching

2018 has been the best year of my career by far. Not necessarily the easiest, but it’s been the year where I have learnt the most about developing my teaching practice. I feel closer than ever to achieving what I call the Pinnacle of Teaching.

The pinnacle? That’s what I call teaching where the highest possible proportion of pupils learn what is being taught on the first attempt. It’s hard, but possible, and I think I got close to it whilst working at Great Yarmouth Charter Academy (Charter).

Charter was the best school that I’ve worked at. It’s the best, I think, because staff are encouraged to work with what Ray Dalio, in his book Principles, called ‘Radical Transparency’. Dalio defines it as “a culture that is direct and honest in communication and sharing of company strategies so that all people are trusting and loyal to the continuous evolution of the organization. For leaders, radical transparency is a way to build trust with their employees.”

At Charter, if I made a mistake I felt I could report it without fear of rebuke or reprisal. A moment of magic or a mistake, the reaction from staff was always supportive, professional and  converted into a learning point. Charter is a school where teachers can openly talk about a mistake they have made in a lesson, or how they could have taught that lesson better upon reflection, or how a lesson went better than expected. This is because the Headmaster, Barry Smith, is unapologetically transparent. Barry is transparent with his teachers, support staff, pupils, parents, the media, you name it. He supports his staff, nurtures them and empowers them. I’ve regularly spoken to Barry or a member of SLT about something that went wrong in a lesson, and how I learnt so much from it, and how I would do things differently. This practice was encouraged, and Barry would regularly share such anecdotes with staff during briefings. You would see the member of staff being mentioned beam with joy for being recognised for their honesty.

The transparent environment gave me the space to challenge orthodoxies and previous pedagogical insights and try other teaching strategies which could (and did) result is greater returns. The return was inching ever closer to the Pinnacle of Teaching. How did I come close to achieving this? The determining factor was pre-emptive planning.

Pre-emptive planning

In my planning, I would prepare worked examples, a parallel set of AfL questions and then create practice exercises for pupils to complete independently. I would try to cover all the possible problem types for a concept, so there would be a teaching sequence where all the pupils would quickly transition from the simple types to the most complex. Importantly, I would allow more time for the harder examples because all pupils need to be given the time and space to tackle a concept in its most complex form.

This pre-emptive planning saved me minutes in every lesson, which ultimately saved hours over the course of the term. I wouldn’t be re-teaching, I was happier, and the kids felt more successful.

From my resources I was able to see and explain

  1. What the children were doing
  2. why the kids were learning what they were learning;
  3. what the children gained from this learning experience
  4. how I knew the children were learning
  5. how the children knew they were learning

With planned resources, I could then focus on my teaching. Once pupils had learnt the material, I focused on helping them to retain what they were learning. This is so important. I tested pupils’ understanding by writing 5 – 7 recap questions on a post-it note, and kids would do these questions on their mini whiteboards at the start of the lesson. These were the hard questions that I knew pupils needed daily practice to prevent forgetting. I would then ask them to complete AfL questions on their mini whiteboards along with a fortnightly quiz to cover the full domain of what they had learnt.

The testing process was about 75% of the teaching process. This doesn’t mean the actual teacher instruction isn’t important. It just means the testing has to be more important. The testing process is the pupils chance to apply what they have understood from the teacher instruction. The learning for pupils starts once they are tested.

I think it’s commonly mistaken that pupils listening to the teacher going through worked examples is the learning process completed. Listening isn’t necessarily evidence that the kids have learnt anything, but pupils listening to the teacher gives the impression they are learning.

In March, I was feeling more successful as a teacher, and my pupils were getting accustomed to the feeling of success. They were learning content faster, and retaining it for longer.

Here are some videos of pupil work (Year 8 set 3/3):



To add a bit of context, I worked in a school that was struggling. Once Barry arrived behaviour rules were enforced consistently, which put the authority back into the hands of the teachers but the pupils that I taught had a shaky foundation of knowledge that I had to re-sequence the scheme of work to teach them the fundamentals: four operations (with Year 7 and bottom sets), negative arithmetic, number theory etc. Only after the first half term of sorting out the basics was I able to make the scheme of work accessible for them. This was a difficult call, but I could do this because I could be honest and say – “the kids haven’t really learnt much from the previous years, if they have, then don’t remember any of it.”

I got to a point where a large proportion of children in each class would complete the AfL questions correctly on the first attempt. Yes, there were some children who struggled to get questions right the first time. However, over time those pupils eventually would get the answer correct on the first question attempt, more frequently. These are the pupils that I think about the most when I am creating resources. How do I make this pupil successful when completing a sequence of questions?

The radically transparent environment enabled me to do my job to the best of my ability. Kids could learn better and were better able to retain their learning. Because this was going on in every classroom the school’s results achieving at least a 4, leapt from 30% to 58% in just one year.

It’s a magical place. Go and visit, Barry and his team would love to have you. The word on Twitter, is that he is looking to recruit Maths Teachers and a new Head of Maths. Get in touch if you are interested.

Read more about the school in these blog posts:

#mathsconf16/17: Atomising

This blog post is a summary of a workshop I ran at Mathsconf16 and 17. The session was called “The Pareto Principle of Lesson Planning” and the rationale was to explore how the Pareto Principle explains that the general relationship between inputs and outputs is not balanced. It can be the case that a small number of inputs can lead to increased outputs I explore this in more detail and use the context of teaching perimeter.

What is the 20% of the input that contributes to 80% of the result?

The 20% input is referred to as Atomising. This is the process where you break down a topic into its sub-tasks. This is a term coined by Bruno Reddy.

The 80% result this achieves is that it allows pupils to develop flexible knowledge of the concept.

Atomising avoids two common pitfalls.  Firstly, it avoids re-teaching. I’ve certainly been in a position where I have taught a unit of work and then realised certain sub-tasks that I could have taught which would have helped my pupils develop a better understanding of the concept. Secondly, you avoid missing out sub-tasks to teach. When you breakdown a topic into its sub-task you avoid missing out certain aspects of a topic which really need to be taught explicitly. Due to the so-called ‘curse of knowledge’, teachers often forget that there are certain decisions and procedural knowledge that we have but which we forget to teach to the kids. Either it is so obvious that we think the kids already know it or, more commonly, we don’t realise which areas of the topic we are teaching pose difficulties for the kids. It could be that the difficulty is caused by a weakness the pupil may have in a different area of maths. For example, if a child is finding the missing side length of a shape, and the perimeter is a whole number, and the sides add up to a decimal, then the area of difficulty may be that a pupil doesn’t know (or remember) how to subtract a decimal from a whole number.

Here are the 12 sub-tasks that I used to break down the topic of perimeter. I chose perimeter deliberately because I think it is a perfect example of a topic which is perceived to be very easy for pupils to learn. However, there are certain aspects of perimeter that I will identify which I don’t think are explicitly taught. I think this because I have seen this to be the case when looking through several secondary maths textbooks.



1)      Perimeter of Irregular shapes

2)      Perimeter of rectangles

3)      Perimeter of parallelograms

4)      Perimeter of regular polygons

5)      Manipulating the perimeter of regular polygons

6)      Manipulating the perimeter of a rectangle – one side length given

  1. Given the perimeter, what is the perpendicular length
  2. Writing the possible side lengths of a rectangle given the perimeter

7)      Manipulating the perimeter of an Isosceles triangle and an Isosceles trapezium

  1. Given the perimeter, what is the size of each equal side length

8)      Perimeter of a compound shape

  1. What is a compound shape?
  2. Perimeter of a L-shape compound shape (irregular hexagon)
  3. Perimeter of non-L-shape compound shape

9)      Manipulating the perimeter of a Compound shape

  1. Finding one missing length of a compound shape – not using the perimeter
  2. Finding one missing length of a compound shape – using the perimeter
  3. Finding two missing lengths (not connected) of a compound shape – using perimeter
  4. Finding two missing length (connected) of a compound shape – using perimeter

10)   Perimeter of Compound shape – combining polygons

  1. Combining regular polygons to form a compound shape – using the perimeter of the original polygons
  2. Combining irregular polygons to form a compound shape – using the perimeter of original polygons

11)   Perimeter: Increased, decreased or stayed the same

12)   Drawing shapes on a square grid

The thinking time that went into breaking down the topic of perimeter took me 10 minutes. I think if I hadn’t gone through this process then I would have certainly missed many sub-tasks. In addition, it would have resulted in me having to do a lot of re-teaching.

Please note that some images aren’t drawn to scale, unless stated.

Example Sets for Each Sub-Task

1)      Perimeter of Irregular shapes

I started to teach perimeter using explicit examples where pupils had to deliberately add all the lengths. They had questions where the side lengths were labelled using integers, decimals (same number as well different number of decimal places), multiples of 10, etc.

2)      Perimeter of rectangles

I started teaching this with all side lengths labelled, then only three sides labelled, then only one pair of perpendicular lengths labelled. Then I included questions where pupils had to deliberately compare the perimeter of two shapes. The questions were designed so it wasn’t visually obvious which shape had the larger perimeter. Here is an example:

An example like the one above forces pupils to add the values because, even though the longest length has increased in size, the smaller length has decreased in size. This question is also designed so the shapes have the same perimeter.

3)      Perimeter of Parallelograms

This sequence was very similar to the sequence for finding the perimeter of a rectangle:

  • All side lengths labelled
  • Three side lengths labelled
  • One long and short length pair labelled, etc

4)      Perimeter of Regular polygons

Here pupils are being taught to calculate the perimeter of a regular polygon using multiplication. They are taught that if you multiply one side length by the number of sides then you can calculate the perimeter.

The sequence of questions shown above demonstrates that we can get the same perimeter despite the polygon changing and its side length changing. I have also deliberately designed the questions to communicate this flexible understanding of perimeter. From the first question to the second, the side length changed. When you move to the third question then the shape and side length change, but the answer doesn’t change. For the fourth question, the side length and shape have changed but the answer doesn’t change.

5)      Manipulating the perimeter of a regular polygon

Here pupils are given the perimeter of a regular polygon, and they know the number of sides each regular polygon has, so they need to find the side length of that regular polygon.

Here is an example set of questions:

Here the perimeter of the shape has stayed the same, but the shape has changed. Here pupils can see that when the number of sides increases, then the side length decreases, given that the perimeter hasn’t changed. They can also see examples where the side length can be a fraction.

I haven’t asked pupils to convert the improper fraction into a mixed number because a mixed number communicates size in a way that an improper fraction doesn’t. A mixed number would communicate more to a pupil about the side length of a square in relation to the side length of the pentagon in the previous question. However, the focus is not in understanding the magnitude of the square and heptagon. The focus here is to get pupils to state the perimeter of a regular shape given the perimeter of that shape. Pupils are practising the procedure of dividing the perimeter by the number of sides of the regular polygon, to find the side length.

Pupils are then asked questions where they are given the perimeter and they must state which regular shape would have the greatest side length. This helps pupils to see that a regular polygon with more sides will have a smaller side length compared to a regular polygon with fewer side lengths, given they have the same perimeter.

For example:

And here is an example where they aren’t given the perimeter at all:

Within this aspect of perimeter, I also created questions where pupils had to find the perimeter of a regular shape knowing that the value of the side length is equal to the number of sides that polygon has. Here pupils are using their square number knowledge to find the perimeter of a regular polygon.

6)      Manipulating the perimeter of a rectangle – one side length given

Here pupils are given one side length of a rectangle and the perimeter of that rectangle. They now need to find the other perpendicular side length. Here they are practising the procedures of:

1)      Double the side length given

2)      Subtract from the perimeter

3)      Divide that by two to find one of the missing side lengths

Here are some examples:

I deliberately put in an example where pupils were doubling an even number for the first example and an odd number for the second example. I deliberately gave pupils the longest length in the first example and the short length in the second example. This is because I want them to see that I have changed the side length but the procedure to find the other length hasn’t changed.

The third example uses a decimal because, when you double it, you get an odd number. When you subtract from the perimeter, you get an odd number, so when you halve the odd number you then get a decimal. I made the question arithmetically more difficult because I knew that in the first two examples the answer would be an even number which is divisible by two. I wanted to make a question where pupils could see that you can get a rectangle with a side length which is a decimal, and not a whole number.

I then moved on to asking pupils to state the different possible rectangles they could make for a specific perimeter. There are many possibilities. I restricted the possibilities by putting in a few conditions. Here is an example:

Here pupils can only give these answers, because the first value is A, and it must be larger than B’s value. In addition to this, I designed the question so pupils had to stop at 7 + 5 to avoid writing 6 + 6 because then the value of A and B would be the same. This is not what the question is asking.

7)      Manipulating the perimeter of an Isosceles triangle and an Isosceles trapezium

Here pupils will practise finding the missing side length of an Isosceles triangle where they are practising the procedure:

1)      Perimeter – base length

2)      Divide by 2 to find the value of each equal side length

The images aren’t drawn to scale. Here are some examples:

Here I deliberately used 8 and 12 in the first two examples to get kids to actively use the procedure to avoid being in autopilot mode. The numbers are similar for this reason. Pupils can then see that as the base length increases between the first and second question, the side length becomes smaller. In the final example I use an odd number for the base number, to deliberately get each equal side length to be a decimal.

Pupils then apply a similar procedure to find the missing side lengths of an isosceles trapezium, but there is an additional step:

1)      Add the known side lengths

2)      Perimeter – total of side lengths

3)      Divide by 2 to find the value of each equal side length.

The images aren’t drawn to scale. Here are some examples:

Pupils here also see that, when the top parallel length increases from the first example to the second example, each equal side length decreases. Similarly, from the second to the third example, when one of the parallel lengths go from 5cm to 4.5cm, each equal side length increases.

8)      Perimeter of a compound shape

Pupils will learn what a compound shape is. They will then find the perimeter of a compound shape. I will use the L-shape compound shape because pupils will eventually learn that if you add the longest horizontal length and the longest vertical length, then double it, you will also find the perimeter of the shape.

Pupils will see questions where they are working with integers, decimals, both etc.

The images aren’t drawn to scale. Here are some examples:

They will then learn to find the perimeter of different types of compound shape. The images aren’t drawn to scale. Here are some examples:

9)      Manipulating the perimeter of a compound shape

Here pupils will first be asked to find the missing length. They won’t be using the perimeter at all. This is because I want pupils to understand which lengths are related to each other, and which aren’t. In the second image, the vertical lengths are related because the longest length subtract the shorter length will find the value of A. These lengths are connected to each other.

Similarly, in the second image, the horizontal lengths are related because the two shorter horizontal lengths sum to give the size of the longest horizontal length. These lengths are related.

So, pupils will first practise finding the missing lengths without using the perimeter at all.

They will then be asked to find the perimeter of the shape once they have found the missing values for A and B.

The images aren’t drawn to scale. Here are some examples:

Here is another example which is rotated to get pupils to still identify the connected side lengths:

And another, finding a missing length for different compound shapes:

I then increase the difficulty in finding the missing length of a coumpound shape. Here we can’t find the missing lengths unless we have the perimeter. This is because the third image has two conneted vertical lengths which are missing.

The images aren’t drawn to scale. Here are some examples:

If the perimeter of the compound shape is 36cm, now I can find both missing lengths.

The images aren’t drawn to scale. Here are some examples:

Questions like these allow pupils to understand the following:

1)      If two connected lengths are missing, then I can only find these lengths if I have the perimeter

2)      Given the perimeter, I must follow this procedure.

I like these questions a lot because I have made the concept more difficult by not combining other perimeter with other concepts, or by making the numbers more difficult. I have taken the concept of perimeter with compound shapes and changed the amount of information given. The difficulty is within the concept.

10)   Perimeter of Compound shape – combining polygons

  1. Combining regular polygons to form a compound shape – using the perimeter of the original polygons

Here pupils are learning to combine different shapes to form a compound shape. Here they see a compound shape being formed and trying to understand what lengths are required and which aren’t required. The images aren’t drawn to scale. Here are some examples:

  1. Combining irregular polygons to form a compound shape – using the perimeter of original polygons

Here we have moved from combining regular shapes to irregular shapes. I must structure the question in a way that one length of the first shape is equal to one length of the second shape. This gets pupil again recognising which side lengths of the two original shapes are required, and which aren’t, to find the perimeter of the new compound shape. The images aren’t drawn to scale. Here are some examples:

11)   Perimeter: Increased, decreased or stayed the same

Pupils are moving onto identifying that the perimeter is something that can change by increasing, decreasing or changing shape, but the perimeter can remain the same.

Here they aren’t being asked to find the perimeter of a shape, but instead they are to say whether the shape has a perimeter which is greater than, smaller than, or equal to the perimeter of the original image. The images aren’t drawn to scale. Here are some examples:

This also allows pupils to see that we can change the image and that the perimeter can change, but it also may not change.

12)   Drawing shapes on a square grid

Pupils are now at a point where they are taking their knowledge of drawing rectangles with a specific perimeter which has been taught in this sequence, but now drawing it on a square grid.

The images aren’t drawn to scale. Here are some examples:

Pupils are then equipped to match a specific perimeter to a specific image. They are applying what they have learnt rather than answering direct questions.








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