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.

Walk each example aloud, one at a time.

• Rectangle — show the long way (add all four), then the smart way (one of each, doubled). Stress that both give 22 cm.
• Square — connect four equal sides to 4 × the side, a fact they already know from tables.
• Pentagon — generalise: when every side matches, multiply one side by how many sides.

After the rectangle's two methods, pause for a thumbs-up settle check: thumbs up if you can see why pairing the equal sides gives the same answer as adding all four. Let that land before you move to the multiplication shortcut for the square, so the two ideas don't blur together.

Pause after the pentagon and ask a pupil to predict the rule for a hexagon before you move 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, do a quick turn-and-name across the room — pupils tell the person beside them which pairing they would add first — 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. The square, triangle and pentagon variations are worked in the Class Challenge that follows — 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 widget 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.