Here is a pictogram where every single child needs their own symbol. The top row alone needs ten symbols, one for each child. That is an awful lot of drawing! What if one symbol stood for two children instead of one?

We build these counts together on a key of two, in order: first 6, then 4, then 5 (the half-symbol one), then 7. One pupil comes up to build each row while the rest of us count on in twos aloud and check the row. Read the key before you start.

First we spot and fix one wrong row together. The key is two. A row is meant to show 7, but it has four whole symbols. Count in twos: that is 8, so it is one too many. Take one whole symbol off and put a half-symbol instead. Three wholes and a half make 7.

Then we work through these on a key of two, in order: fix a row, build a row for 10, fix a row (watch for the half-symbol), then build a row for 11. One pupil takes the board for each round; the rest of us work out or read the count in twos and agree the answer before we press Check. Each one is a step trickier than the last.