Take two or three hands-up answers, not open call-outs. You are fishing for the words bigger and twice or double — hold out for the idea that both the height and the width grew, and by the same amount. Do not reveal the term scale factor yet; that lands in the next step.

• Rectangle ×2 — count the grid squares along each side of the copy against the original; draw out that both sides doubled, so the multiplier is the same for every side. Name it: this multiplier is the scale factor.
• Triangle ×3 — ask what stayed the same. The corners (angles) are unchanged; only the lengths grew. This is what "keeps its proportions" means.
• L-shape ×2 — the shape is still the same shape, just bigger. Head off the common slip: enlarging is not "add the same amount to each side" — it is multiply each side by the factor. Pin it on a side of 3 squares: adding 2 gives 5, multiplying by 2 gives 6.

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

Start with the rectangle ×2, then ×3; then switch the shape to the triangle for ×2 and ×4. Before each enlargement, ask the class to predict the new length of one named side. Watch for the pupil who says a side "went up by 2" instead of "was multiplied by 2" — pin the difference on a side that is 3 squares long: adding 2 gives 5, multiplying by 2 gives 6. Only one of those keeps the shape.

Practice round: pupils take turns at the interactive, class confirms each match before moving on. Keep it brisk.

Worked example (after the L-shape, before ×4) — board the two lengths, method end to end:

• Original side = 2 squares, image side = 8 squares.
• Scale factor = image ÷ original = 8 ÷ 2 = 4.
• Repeat on a second side so the class sees every pair gives the same factor.

Slip to watch: subtracting (8 − 2 = 6) or dividing the wrong way round (original ÷ image). Pin it: we always divide the new length by the old length.

Then run the ×4 triangle challenge so they use the factor they just found.