Take two or three hands-up answers, not open call-outs. Listen for anyone who says measure round the edge and add it up — that is exactly where the lesson is going.

Work each one live — trace round the edge with your finger and add aloud as you go.

• Rectangle — draw out that the two long sides match and the two short sides match, so 2 × (6 + 4) is a quick check.
• Square — hold out for a prediction before the reveal; the class often expects a bigger number, then sees it lands on 20 as well. That is the surprise worth naming: same perimeter, different shape.
• L-shape — this is the one where adding all the sides really matters. When you name the word composite, point to how the L is really two rectangles joined. The slip pupils make is missing the two short inner sides at the corner. Count the sides together — there are six.

The interactive opens on the 5 by 3 rectangle. You reshape it live by dragging the corners to stretch it to 7 by 2. Bring a different pupil to the board for each rectangle so the turns are shared across the room.

Before you read the perimeter off the screen, get the class to add the sides aloud first, then check against the readout. On the 7 by 2 shape, watch for pupils who add only two sides (7 + 2 = 9) rather than all four; ask have you walked the whole way round?

After the rectangles, look back at the L-shape from Watch and Notice and ask what the perimeter would be if it were a plain 6 by 5 rectangle instead. This sets up the wrap.

This is the practice round — real objects and the printed sheet are measured at desks, and the class confirms each reading aloud at the end. Circulate and catch slips on the spot.

The L-shape is where pupils lose sides — remind them to count how many sides they have before totalling. On the printed polygons, watch for reading the ruler from the 1 mark instead of the 0 mark. The desk top may need the tape laid twice; help groups add the two lengths. Fast groups move on to the hexagon in the stretch task.