Display a simple 5 cm × 2 cm rectangle on the board with the top and one side labelled. Take three hands-up answers, not open call-outs. Listen for a pupil noticing that opposite sides match — revoice it as the top equals the bottom, and the two sides are the same too. Don't reveal the shortcut yet; that lands in the next step.

Rectangle 7 by 4: long way 7 + 4 + 7 + 4 = 22 cm. Then the smart way, pair the equal sides: 7 + 4 = 11, doubled 11 + 11 = 22 cm. Stress both give 22.

Thumbs-up check: can they see why pairing the equal sides matches adding all four? Let it land before moving on so the two ideas don't blur.

Square side 9: four equal sides, so 4 × 9 = 36 cm rather than 9 + 9 + 9 + 9. Link to tables they know.

Pentagon side 5: five equal sides, 5 × 5 = 25 cm. Generalise: equal sides means multiply one side by the number of sides.

Pause and ask a pupil to predict the rule for a hexagon before moving on.

This round is for talking it through together. A pupil names the equal sides at the board, then the class agrees the quickest way to add them.

Ask the pupil at the board to name which sides are equal before adding (top and bottom are both 6 cm; the two sides are both 3 cm). Between the naming stage and the adding stage, take a quick hands-up prediction from the room — which pairing would you add first? — and hear two pupils, so the watching class stays with it. Then take the addition: 6 + 3 = 9, doubled is 18 cm. Revoice it as two of each, so add one pair and double it. If a pupil still adds all four one by one, accept it as a check but push them to also show the paired version. Keep this beat to the single rectangle so the on-screen shape and your words stay in step.

The square on screen (4 × 4 = 16 cm) is the first challenge. Once the class has it, draw the other three on the board in turn — the interactive shows one shape, so the rectangle, hexagon and octagon are quick teacher sketches with their side lengths labelled. Pupils take turns naming the equal sides and the class confirms before moving on. Keep it brisk.

For each shape ask which sides are equal, and how does that speed up the adding? Answers: the 10 × 6 rectangle is 2 tens and 2 sixes, so 20 + 12 = 32 cm; the regular hexagon is 6 × 5 = 30 cm; the regular octagon is 8 × 7 = 56 cm. The hexagon and octagon are the stretch — fluent pupils reach for the multiplication straight away. The 10 × 6 rectangle is the one to watch for the slip of multiplying instead of pairing; revoice it as two tens and two sixes.

Keep this brisk. Re-state the one big idea: equal sides let us multiply instead of adding slowly. Flag the shift coming next from perimeter (around the edge) to area (the space inside) so pupils don't muddle the two.