Look at these three shapes on the board: a square, a triangle and a hexagon. Every corner is a little turn from one side to the next, so every corner is an angle. Hands up: which shape do you think has square-corner angles like the corner of a window?

Look at each shape and its corners. Every corner is an angle. We will also bring in a rectangle here, a new shape, so we can compare its corners with the square's. For each shape, look at its corners and be ready to say how many there are, and whether each one looks like a square corner, a sharper corner, or a wider corner.

Then check the corners of these shapes in turn: a square, a triangle, a wide triangle, and a rectangle. Slot the paper corner into each one and see if it fits exactly, or is too small, or too big.