Look at these muddy wellies lined up outside the classroom door on a wet day. We need to count them. Must we count every single boot, or is there a quicker way? There is a clever shortcut hiding in those pairs.

Six pairs of wellies. The shaded cells are 2, 4, 6, 8, 10 and 12: one shade for each pair. Each number is two bigger than the one before.

Here is the same pattern all the way to 20. Ten pairs: 2, 4, 6, 8, 10, 12, 14, 16, 18, 20.

The pattern stays the same past 20. This board shows jumps of two shaded toward 50. Look down the columns: do any numbers sit one under another?

We will chant in twos together. One friend shades the next number on the hundred square, but we pause first so you can guess the next number before we shade it.

Your turn on the board. We are counting in twos. Shade the next number the prompt asks for. On the last one, shade three jumps of two. Which numbers do we skip, and why?