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What is it?
This is the first secondary school maths lesson our lovely new bunch of Year 7s experience each September, and I absolutely love it. All the students need to be able to do is to subtract one number from another – and yet there is so much more going on! I love this activity because it perfectly fits that all important definition of “low barrier, high celling”. Students can grasp the rules easily and hence make some progress with the task in the first 20 seconds, and yet there is enough meat in this activity to keep them thinking about Diffy for weeks to come!

How can it be used?
We have had most success with this task by starting everyone off on the same structured example, so that students are familiar with the rules, and then giving them a choice of things to investigate. Some of my favourite lines of inquiry are:

– What do Diffy 2s have in common?

– Can you make a never-ending Diffy?

– Is it true that if all the numbers are under 5, you never get more than a Diffy 3?

There are loads more prompts and lines of inquiry in the comments section on the resource page, and it would be great if you could add some more.

I hope you and your students enjoy it

Craig Barton

Download Diffy

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