Take three hands-up answers for the edge (expect 100 cm), then let the second question hang. Do not confirm the total yet.

Listen for the common wrong prediction of 100 for the whole square, that is the misconception this lesson exists to fix. Note it without correcting; the grid in the next step settles it.

Hold on the first grid until the class sees the two edges are each 100 cm. Ask how many along one row, how many rows? before revealing the product.

The pivot is here: 100 along and 100 up gives 100 × 100, not 100. Say the length scaled by 100 and the breadth scaled by 100, so the area scaled by 100 twice.

On the 2 m² grid, point out the two halves as two separate square metres before revealing the total, so the class reads it as two square metres and not one long strip. Ask the class to predict the total before you point at it. Revoice a pupil who says "double 10,000".

Talk this one through together, pupils take turns at the board and the class agrees or corrects out loud.

What is on screen: only the edge ladder (m ↔ cm). Use it to confirm the edge conversion is × 100 down / ÷ 100 up. Reset the From value manually for each round: run 1 m → 100 cm, then 100 cm → 1 m, so the class sees both directions.

Then step off the ladder and work at the board (the ladder does not show area units, so keep this board work separate and say so): build the area factor 100 × 100 = 10,000, then work the four area conversions by hand: 3 m² = 30,000 cm², 25,000 cm² = 2.5 m², 0.5 m² = 5,000 cm², 40,000 cm² = 4 m². For 0.5 m², hold out for the prediction before you confirm. The common slip is 50,000 (multiplying half a metre as if it doubled) or dropping to 500; the correct answer is 5,000 cm², exactly half of 10,000.

Keep reminding the class: the edge factor is 100 but the area factor is 10,000, because area carries the square. This is the point the whole lesson turns on.

Run the edge conversions on the ladder first (pupils take turns at the board, check each answer, the class confirms before moving on). All three are everyday classroom lengths: 4.2 m → 420 cm, 250 cm → 2.5 m, 3.5 m → 350 cm. Keep the board work brisk rather than over-explaining. These edge rounds keep the × 100 / ÷ 100 rule warm.

Then build the tiling problem on the board, off the converter, because the converter cannot show a division. Draw it out step by step: one tile is 25 × 25 = 625 cm²; 1 m² is 10,000 cm²; so 10,000 ÷ 625 = 16 tiles. This is the key one that ties the 10,000 fact to a real building job. Let a pupil reason it aloud before you confirm.