Take two or three hands-up answers, not open call-outs. You are fishing for the misconception that pupils want to right-align the digits the way they do with whole numbers. Don't correct yet — let the wrong idea sit, then say let's see what the columns tell us and move to the model step. Five seconds of quiet think-time before any hands go up.

Walk each example one at a time

• 3.4 + 0.275 — point to the empty hundredths and thousandths columns in 3.4 and say we fill these with zeros so they are not left blank. This answers the hook directly.
• 12.06 + 5.349 — pause on the carry; the hundredths make ten, so ask where does the little 1 go? and confirm it lands above the tenths, not the units.
• 8.5 − 3.726 — narrate the borrow slowly across the tenths and hundredths.
• 10.0 − 4.085 — this is the trickiest; let the class watch the borrow travel through the zeros before you reveal the answer.

Do not rush. The trailing-zero habit is the whole lesson.

This round is for talking it through together — a pupil works at the board and the class agrees or corrects out loud.

Call a pupil up. Insist the first move is line up the points and fill the gap with a zero — do not let anyone start adding until the columns are square. Have the rest of the class watch and call out if a zero is missing. Watch for pupils who put the answer's decimal point in the wrong place; the point in the answer sits directly under the points above it.

If time allows, write two more on the board by hand and call up another pupil each time, keeping the same first move: 7.025 + 0.9 (fill 0.9 out to 0.900) and 9.4 − 2.18 (a take-away — fill 9.4 out to 9.40 and borrow across the tenths).

This round is the practice bank — a pupil works each one at the board, the class checks the answer, and everyone confirms before moving on. Keep the board work brisk rather than over-explaining.

The borrowing through zeros in 15.0 − 6.074 catches people out; have the class predict before the pupil at the board works it. The final challenge is the stretch — the missing number is what you take from 9.5 to land on 3.275, so the class can reason it as 9.5 − 3.275 = 6.225 and then check that 9.5 − 6.225 really does leave 3.275. Strong pupils who finish early can mouth the next column or simply watch; they do not have desk work in this step.

A quick verbal recap is enough here. Re-state the three-step habit — line up, fill with zeros, work column by column — as the thing to carry into the activity book practice.