Trace a finger right around a rectangular page on the IWB, ending back at the starting corner. Take two or three hands-up answers, not open call-outs. Listen for add up the sides or measure all the way round — that is exactly where the lesson is going.

Walk each shape aloud, touching every side in turn and saying the running total.

• Triangle — touch 3, then 4, then 5, landing on 12 cm. Stress that each side is counted just once.
• Square — all four sides are equal, so it is four lots of 4 cm. A first gentle link to multiplication, but keep it as addition here.
• Rectangle — name the long pair and short pair, then add all four sides to reach 16 cm.

The make-or-break point: every side is added exactly once, and no side is missed or counted twice.

This round is for talking it through together — one pupil works at the board while the rest of the class reads and totals aloud, agreeing or correcting.

Call a pupil to the board to touch along each side of the shape in turn while the class reads each length aloud and keeps a running total. Watch for anyone who skips a side or counts a side twice — revoice with did we touch every side exactly once?. Rotate three or four pupils across the rectangle and then redraw it as a square and an L-shape so the class sees the same rule on different shapes.

This round is the practice bank — real objects circulate around the room (or sit at stations) and pupils measure each one with their own string and ruler. Keep the pass-on rhythm brisk; the class confirms each reading aloud at the end.

Hand out cards (about 4 cm by 6 cm), string, rulers and the Perimeter Measuring Record sheet. Sub-prompts of rising difficulty: find the perimeter of the card; find the perimeter of your own copybook to the nearest centimetre; find the perimeter of a triangle card; then compare two cards by holding the first card's string around the second card's edge to predict which is longer, then check by measuring. Watch for pupils pulling the string tight enough to follow the corners but not stretching it. The class confirms each reading aloud.

Keep the recap brisk. The next lesson builds straight onto today by using the equal-pairs property of rectangles to find missing sides.