A Maths Event in London #LateMaths

I’m very pleased and excited to announce that on Saturday October 27th I will be taking part in a maths inspired evening open to all in London. I’ll be launching my latest book, ‘More Geometry Snacks’ published by Tarquin Publications alongside my amazingly talented co-author Vincent Pantaloni. It’ll be the first time I’ve actually met Vincent after working on two books together from afar! If Geometry Snacks missed your radar, you can read about it in the Guardian here or Aperiodical here, or most recently, this lovely article posted a few days ago by Sunil Singh.


Anyway, the followup is coming out in time for Christmas, and we’ll be including a free signed copy to people attending the event.

The Venue:

The event will take place at a book-themed bar called The Fable in Farringdon, London. Easily accessibly by public transport:

52 Holborn Viaduct, London, EC1A 2FD

The evening will start at 6pm and include a variety of talks and activities, as well as food and drink! Both Vincent and I will be talking about some of our favourite things about mathematics, and we’ll be joined by the wonderful Ben Sparks of Numberphile and Maths Inspiration fame!

Activities will also be provided by the fabulous Think Maths team, Matt Parker, Katie Steckles and Zoe Griffiths


Excited? You should be! It’s an amazing line up and I can’t wait!!

To book your places, click here. Tickets are £29.50 + booking fee and include a free signed book and food as well as all the provided entertainment.

The event will be hosted by Jo Morgan (@mathsjem) who has an excellent dedicated webpage for the event here. I hope to see you there for an amazing night of maths-based entertainment and fun!



Year 7 Maths – A Missed Opportunity?

One thing I’ve noticed more and more recently is how out of sync the transition is for mathematics students leaving primary (grade?) school and starting secondary (high?) school. I’ve worked in, and visited, a large number of schools at this point, and although certainly not always the case, I’d comfortably say the majority of schools I visit follow very similar, and in my opinion, flawed, year seven programmes for their eleven year olds.

Typically (I should be cautious using that word), students arrive on day 1 and are placed in mixed groups for the first few weeks. This period can last anywhere between two and six (!) weeks. This period is effectively a holding cell until departments determine the ability of each child according to their own internal tests and assessments, despite the fact that students are coming in with a lot of maths data attached to them from primary. The reasoning behind this is often cited as standardising across groups who have come from different schools, or protecting against students performing well or poorly in their final assessments in primary school, but not performing consistently at that level. Cynically one might say that this is all really about not trusting the data they come in on…

Once the students are finally re-assessed in Year 7 – which could be anything from a single test to three or four, students are then placed into sets – which could be anything as strict as a class-by-class hierarchy, or (my personal preference for what it’s worth) loose setting with three ‘bands’ that are essentially mixed within a couple of grade boundaries.  Now I should reiterate that this is just what I’ve experienced, and certainly does not speak for the entire English school system, but as I said, I’ve seen a lot, and they usually fall into some kind of version of this structure. I’m really interested to hear about alternative approaches in the comments.

So what do students *do* in this interim period? Well, again, it differs, but often it’s looking at the basics of numeracy – number operations, proportion work, fractions etc. This in part is to help prepare them for the assessments, but also acts as a testing ground to see if students stand out as being higher or lower achieving than their data suggests. It can be completely detached from any kind of scheme of work or curriculum. I hear a lot about students ‘going backwards’ or ‘standing still’ in this time, simply because they (most of them) aren’t learning anything new, and much of what they’re being taught, or are revising, is stuff they did to death, successfully, at primary school.

At this point I should add a little balance. I’m not bashing teachers, and I understand that there is some truth when I’m told “they *should* know that stuff, but often they don’t, or they’ve forgotten it”, so perhaps this time is not wasted as such. In fact, in my own teaching experience I have frequently found that to be true with a lot of children, (but also false with others!). Certainly, if this entire process takes place over a week or two, then the implications of ‘not moving forwards’ are fairly light – the end justifies the means and all that. However I also feel that with all the massive overhauls of the primary curriculum, and the remarkable work primary teachers are doing (under impossible pressures I might add) with the new maths programs everywhere, that times have simply changed. Is a review needed? I think so.

What I’m seeing and hearing now is that Year 7 students coming into Secondary schools are, in general, much stronger at maths. They have a better conceptual understanding and ability with number. Of course not *all* of them, and of course there will be some areas where this difference is less obvious than others, but I do think the changes are having the desired effect. We could argue about the costs of those changes to everything else, but that’s not what I’m focusing on here.

With those changes in mind, the second thing I’ve noticed is that the entire Year 7 scheme of work is often blind to the new primary curriculum, which has been in place a number of years now. I don’t want to keep using anecdotal evidence here, so let’s take a look at an actual scheme side by side with the primary programme of study.


Year 7 a

The picture above is taken from a scheme of work for Year 7 which is freely available on TES. A few disclaimers: anyone can put anything on TES. This was uploaded in 2010, but was updated in 2014. It has reviews from as recent as a month ago, so it is being used. It has been downloaded 20,000 times. There are more detailed breakdowns of the topics, differentiated etc but this is the broad overview.

From September to January there is literally nothing on there that isn’t taught at primary, several times over six years. Furthermore, almost all of it was taught at primary (several times across the six years) BEFORE the curriculum changes.

scheme 1

One could argue that we need to reteach things all the time (I agree), but typically we’d reteach it and add more content, go deeper, expand the concept. The above is taken from the Year 5 programme of study. It involves composite shapes, and is therefore arguably more advanced than what is listed in the Year 7 scheme of work (point 9).


Above is part of the Year 6 programme of study. It seems a lot more advanced than fundamental concepts of arithmetic using fractions (point 10), which is taught in January in Year 7 (for the scheme I’ve posted).

I won’t keep comparing, you get the point. The Key Stage 1 & 2 Maths Programme of Study is available here. 

Many schools have fantastic schemes of work for Year 7, I have no doubt about that, and if you’re reading this thinking ‘yeah but we dont do that, this is rubbish’ then great, clearly you’re one of those schools.

All I’m trying to put across is that times have changed, and the Primary curriculum should, I think, feed directly into the Secondary one. The gap between Year 6 and Year 7 is no bigger than Year 5 and Year 6, so students aren’t forgetting anything more than they would normally. If you’re in secondary and aren’t familiar with the new (not that new now) programme of study, it’s well worth a quick read – particularly the Year 5 and 6 parts.

Any interesting contributions about how you structure your scheme of work (and your groups) in Year 7 are most welcome in the comments.

Garfield’s Trapezium

James Abram Garfield was a member of the United States House of Representatives when he submitted a proof of the Pythagorean Theorem to the New England Journal of Education in 1876. He of course went on to become the President of the United States. His proof (shown below) was unusual in that it used a trapezium (trapezoid for US readers).

garfield trap1

It’s a straightforward proof to follow, and can be used quite easily in the classroom with a little guidance. But a trapezium structured like this offers so much more than just (just!) a proof of the Pythagorean Theorem.

Take the following configuration, which also shows the enclosing rectangle:


This allows us to investigate angles and determine some properties of the inverse tangent function, arcTan:


In fact you can use Garfield’s Trapezium to derive a whole host of trigonometric functions. Take the example below, which enables you to fairly easily find the tricky trig functions of 15 and 75 degrees:


Fun! As a challenge to you, can you use Garfield’s Trapezium to derive the addition and subtraction formulas for Tan?

Geometry Snacks

I’m very pleased to announce that my second book, Geometry Snacks is now shipping from Tarquin Publications. The book is coauthored by Vincent Pantaloni, a fantastic French mathematician who helped design over 50 geometric puzzles as well as some of the creative solution approaches to each one.


Geometry Snacks is a mathematical puzzle book filled with geometrical figures and questions designed to challenge, confuse and ultimately enlighten enthusiasts of all ages.

Each puzzle is carefully designed to draw out interesting phenomena and relationships between the areas and dimensions of various shapes. Furthermore, unlike most puzzle books, we offer multiple approaches to solutions  so that once a puzzle is solved, there are further surprises, insights and challenges to be had.

As a teaching tool, Geometry Snacks enables teachers to promote deep thinking and debate over how to solve geometry puzzles. Each figure is simple, but often deceptively tricky to solve – allowing for great classroom discussions about ways in which to approach them. By offering numerous solution approaches, the book also acts as a tool to help encourage creativity and develop a variety of strategies to chip away at problems that often seem to have no obvious way in.

The inspiration for the book came from the responses to puzzles I have created here, and the different ways in which people solved them. Take the figure below for example:


(not included in the book!)

This puzzle requires you to find what fraction of the whole regular shape the shaded section represents (constructed using midpoints).

Here is one possible solution:


You can see that the pink area covers half of each vertical pair of rectangles, and that is equal to 4 of the congruent triangles. So the answer must be 4/12 = 1/3

But there’s more life in this puzzle yet! Can you see an alternative approach? Can your students?

How about this submission:


Shearing the parallelogram into a rectangle, then reconstructing the entire shape into a quadrilateral! It’s a lovely approach, and one I wouldn’t necessarily think of myself.

By sharing multiple approaches both to the reader and potentially with a class, everyone learns from new insights and styles of problem solving in geometry – and each puzzle teaches us something new even if we can solve it!

As such each puzzle in the book includes at least 2 solution approaches.

If you have enjoyed my puzzles over the last five years, consider buying this book. It ships internationally, and I think you’ll like it a lot.

Unit Conversion

I have often found that students really struggle to understand what is going on when we convert units of area and volume. It’s pretty straight forward to demonstrate conversion of units of distance: 1 metre = 100 cm etc just by using simple instruments like a ruler or metre stick, or measuring tape. Whilst some may initially struggle with this, really it’s just a question of scale / ratio etc.

When dealing with area however, it gets a lot more confusing. 1 m2 is frequently misunderstood as being equivalent to 100cm2. It’s understandable why: it feels intuitive, and maps nicely against existing knowledge that 1m = 100cm. Unpicking this misconception can be tricky. In what I’d consider to be the least appealing scenario, students are left just memorising that they multiply/divide by the conversion ratio ‘squared’ so 1m2 would be equivalent to (1 x (100)2) cm2 and so forth. This, as stand-alone information, feels a little empty – and of course I’m keen to expand on why this works. The most common explanation I’ve seen is using a diagram of, say, a square (below is taken from BBC Bitesize):


I have no issue with this explanation. It makes sense and it helps students overcome the somewhat counter-intuitive result upon first inspection, that 50000cm2 = 5m2

However, what I’ve often found is that even with this explanation, students resort back to making the same misconception/error regardless of demonstrations to try and make it feel more intuitive. Perhaps then, the issue needs to be tackled further by adjusting the way in which we approach these problems.

Take the following example:

“Convert 250cm2 to mm2

Students who get it right will (again, in my experience) typically mull it over, recall something about areas being a bit different to distances, and then decide upon a multiplier. They would literally write down 250 x 102, or 250 x 100, then arrive at the answer and move on.

I prefer a pictorial approach, which I’ve found tends to bring out more right answers from those other students, and maintains the intuitiveness of the answer being right.

Forget the conversion element of the question for a moment. We are dealing not just with a number (250), but an area of 250cm2. We can represent that as follows:


This gives us our required area.

Now convert the units for each side into our new units, millimetres:


Our rectangle is the same size, it has the same area, and the lengths are unchanged. We’re just using equivalent amounts in different units of measure.

So now the area, which is unchanged, is represented as 250 x 100 = 25000mm2

Students would literally draw both rectangles, one below the other like so:


Now, all is well and good so far, however, what if we get a question like this:

“Convert 17m2 to mm2

17 is prime, and less easy to put into a nice rectangle. Or is it? In fact, this gives us the perfect adaptation to the rectangle representations. Rather than continuously adapting the heights depending on the numbers we’re given in the question, just make them all of height ‘1’, forever, for every question:


“Convert 25mm2 to cm2


The idea can be further adapted for volume conversions:

“Convert 3m3 to cm3


Helping trainee teachers

I often get asked by new mentors how best to help trainees on placement in their departments. It can be daunting for many reasons – you want them to excel, you want them to have a good and supported experience, but you may be worried about how much work you have to put in and how much time you actually (don’t) have. I thought I’d share some key ideas here.

  1. Time
    The most fundamental thing you need to give to a trainee is time. Time for them to develop, but also your own time to work with them. They are unlikely to get better if they are not being guided or being given advice and support with planning. There is a balance to be had here. Pointing them towards the shared resources folder on a computer isn’t nearly enough, but sitting and going over every single lesson plan in fine detail with them is far too much. They are adults and should be treated as though they can do a lot on their own once they’re enabled (although some trainees struggle with this initially!) – but they’re also new to this so they’ll need more support and reassurance that what they’re doing is right (or wrong) in the early stages. Allocating time on their timetable as ‘mentor meeting’ or similar is essential. Trainees typically struggle when their mentor meetings are ad hoc and therefore often on different days / times. This inevitably leads to weeks where there is no meeting at all. If you can, have lunch with them too as this can serve as an informal opportunity to raise or discuss any issues or queries.
  2. Give them a balance of classes
    Don’t give a trainee all the best behaved classes, or all the worst ones. Tougher classes are good to develop behaviour strategies that are less essential to survive in a class where the children rarely stray off task (although bad teaching can cause any class to do that!). A typical strategy is to give them one tougher group, and, if possible, a pair of the same year group to allow for easier planning / more obvious requirements for differentiation strategies (eg if you give a high ability group and a middle/ low ability group in the same year – the topics will likely be the same but the pitch will often be different). That of course assumes classes are setted in some way, which is still pretty common in maths.
  3. Hold them to account
    Some trainees can initially struggle with the difference between being a student, and being a trainee – they are to be treated as if they were an employee at the school, so if they are ever late / miss deadlines / slow to respond to emails etc, hold them to account for that. Similarly, whilst it’s expected that they will make mistakes in the classroom, if they do not respond to feedback – eg, you tell them they need to do something different, and they ignore it, then again, hold them to account for that.
  4. Give actionable feedback
    It’s easy to give feedback that makes sense to you, but no sense to a trainee. “Improve your behaviour management” for example, or “be more consistent with behaviour systems”, or “make differentiation more explicit” . All of these can feel clear, but all a trainee will be thinking is ‘how?’. So tell them how. Give them one or two specific actions that they can follow. For example “give students a choice of difficulty for the main task” or “ensure there are two extension tasks available – one exam style question and one algebraic generalisation question”. These are far easier to follow, especially if you provide examples too. Behaviour targets are particularly difficult to implement. How do I be more consistent? What is inconsistent at the moment? A good way to overcome this, is to ensure you are having regular conversations about behaviour. Scenarios and post-lesson discussions such as ‘when student x did this, I would have done this instead’ or ‘when student x did this, that warrants a C1’ etc. Trainees understandably struggle with knowing what actions in a class constitute suitable escalation of behaviour systems, especially when those systems are themselves sometimes nuanced and flexible (rightly or wrongly).
  5. Observations
    Try to give a mix of general full lesson observations and targeted foci. For example, you might watch a lesson and give feedback on all elements of it, but often that can be overwhelming for a trainee when you inevitably give and discuss ten points of improvement. Often it can be more effective to focus on only one or two particular things, eg behaviour, or quality of tasks. If you can film lessons, then seriously consider it. Watching a lesson back and being able to stop it and discuss is probably the most effective tool you can use to develop a trainee. Don’t be afraid to give live feedback during a lesson either. It’s much better to signal to a trainee that a student is off task, or that a student needs a target to keep them focused, or to praise a particular student for something they did during the lesson, than to tell them they should have done it afterwards. Obviously this requires forethought. Yelling at the teacher “John is off task, sort it out” is unhelpful! You could develop a simple signal system, or discreetly call the trainee over when students are on task etc. I’ve never understood why observers (myself included at one time) watch a lesson go to shit in those instances where they could have subtly intervened and helped avoid it with just a few simple signals. Obviously this isn’t always possible, but moreoften than not, a little live feedback can steer a lesson into a better direction. Remember too that if they are observing, they’ll need training on what to look at / for, and a post lesson discussion explaining the decisions the teacher made. Without those, the trainee will often become a simple spectator or even a pupil in the room.
  6. Planning and Marking
    Give trainees all the tips and shortcuts that you use yourself. We all know that marking policies in some schools are completely unwieldy – how do you manage it? Simple tips such as marking a little during a lesson, carrying around a multipen for those ridiculous marking in green / red / purple things you may be expected to adhere to, collecting books in with the page open that students were working on, in ‘confidence’ piles to help prioritise who needs the most marking etc. Those tips may seem trivial, but if they’re the difference between marking for an hour and marking for three, then they really are significant. One of the hardest lessons for a trainee is learning when a lesson is planned ‘enough’. Typically trainees will overplan a lesson, and refine it over and over again – then they despair that it took them 3 or 4 hours to plan. Learning that the lesson would have been almost, if not just as good, much earlier and that all that extra time is effectively time wasted, is hard. Lesson templates can be useful, as can giving trainees two or three websites to source material from rather than the seventeen billion that currently exist online. If they can’t find what they want in those two or three sites, then start creating. Early on, I frequently find a trainee who has spent upwards of two or three hours looking for a perfect resource that doesn’t exist. Trainees will need guidance and support on this – which is best done face to face if time allows for it. Email feedback can often end up being a constant back and forth of minor refinement in the wrong directions – costing an enormous amount of time for both trainee and mentor / host teacher. And don’t hold back with sharing resources. I find it less and less now, but a few years ago I would still come up against mentors who would refuse to hand over their resources because ‘I never had them when I trained – I had to do it all by myself’. Honestly, we need people to join teaching and stay, not leave because staff are trying to make it more difficult!
  7. Keep in touch with the trainee’s provider based mentor.
    No-one has a more vested interest in the success of a trainee than their university / school direct / scitt mentor. If you have any worries / concerns, or even better, want to celebrate the success of a trainee, let them know! It’s much harder to bring a trainee back from the brink than it is to intervene early on, even if it’s just something really minor. Similarly, it’s always great to hear that a trainee is getting on really well, particularly in those early weeks when they start teaching new groups.

Finally, remember that trainees all start from different places. It doesn’t matter how good or bad they are in their first lesson (within reasonable expectations!), what matters is that they respond to feedback and continue to get better and better.



Trig Identities #4 Double Angles

Starting with one of our ‘sum and difference’ identities:

\sin(x\pm y)=\sin(x)\cos(y) \pm \cos(x)\sin(y)

If we take \sin(2x) = \sin(x+x)

then, using the identity we started with:

\sin(2x)=\sin(x)\cos(x) + \cos(x)\sin(x)

\sin(2x)= 2\sin(x)\cos(x)

We can do it all again with cos:

\cos(2x) = \cos(x+x)

\cos(2x) = \cos(x)\cos(x) - \sin(x)\sin(x)


Now, recall that \cos^2(x) +\sin^2(x) = 1

\cos^2(x) = 1 - \sin^2(x)


\cos(2x) = 1 - \sin^2(x)-\sin^2(x)

\cos(2x) = 1 - 2\sin^2(x)

That’s one identity, now if we go back to the start and manipulate it all a bit differently:



\cos(2x)=\cos^2(x) - 1 +\cos^2(x)

\cos(2x)=2\cos^2(x) - 1

Finally, tan is pretty straight forward if you use the sum&difference identity, but we haven’t derived that yet, so here we go:


\tan(x + y) = \frac{\sin(x+y)}{\cos(x+y)}

Using the sin & cos sum/difference identities:

\tan(x + y) = \frac{\sin(x)\cos(y) + \cos(x)\sin(y)}{\cos(x)\cos(y)-\sin(x)\sin(y)}

= \frac{\sin(x)\cos(y) + \cos(x)\sin(y)}{\cos(x)\cos(y)-\sin(x)\sin(y)} * \frac{\frac{1}{\cos(x)\cos(y)}} {\frac{1}{\cos(x)\cos(y)}}

= \frac{\frac{\sin(x)\cos(y)}{\cos(x)\cos(y)} + \frac{\cos(x)\sin(y)}{\cos(x)\cos(y)} } {\frac{\cos(x)\cos(y)}{\cos(x)\cos(y)} - \frac{\sin(x)\sin(y)}{\cos(x)\cos(y)}}

\tan(x + y) = \frac{\tan(x)+\tan(y)}{1-\tan(x)\tan(y)}

Phew! Now, if x and y are equal, then just call them both x:

\tan(2x) = \frac{\tan(x)+\tan(x)}{1-\tan(x)\tan(x)}

\tan(2x) = \frac{2\tan(x)}{1-\tan^2(x)}