In all the years that I have known Seager he still manages to pull “a blinder” that takes me by surprise and today was one of those days. I’d asked him for an idea to use with year 7 which involved them just “playing with numbers”. It was their first proper lesson having done the whole introduction stuff yesterday and I wanted something that wasn’t too taxing because I wanted to focus on those eureka moments and the joy of solving problems whatever format they may be.

His idea was one that he has been using for years (sorry I can’t credit the original source because there must be one – he genuinely cannot be this creative!). It’s a 3 by 3 grid and using the numbers 1 to 9 only once each row and column add to 15 … sounds simple enough doesn’t it? However, the lovely thing about this was the extra dimensions that could be added to it. The next level is obtained by adding the condition of one of the diagonals summing to 15 too and then the final level is that BOTH diagonals add to 15 (needs to have a 5 in the central square for this. If a student chooses 5 on their first attempt you can use the reverse logic i.e. find a solution where only one diagonal adds to 15, then no diagonals adding to 15.

I’ve tried to summarise it in the picture below:

Like I said I used it today with my year 7 – we did it in the back of their books where we do our “Mrs M won’t mark this bit” work so they could make as many mistakes and crossings out as they needed. It led to discussions about number bonds and the “pairs” adding to get to 10 when 5 was in the central square – were I to have longer I know I would have wanted to take this on to look at why certain “central” numbers wouldn’t work i.e. if 1 was in the middle there is only 9,5 and 8,6 as possible pairs and given that you need more “pairs” than these 2 we can eliminate this as a possibility.

Such a simple yet elegant activity. I suppose if I were a more academically minded teacher instead of one that just flippin’ teaches ’em stuff I’d probably have the urge to call this “low entry – high ceiling”. But I’m not … I just loved the possibilities.