Take three hands-up answers, not open call-outs. Give five seconds of quiet think-time first. Do not confirm yet — hold out for the reason as well as the yes/no, then move to the board.

These scales add the blocks on each pan, so we keep them to additions and subtractions; the multiplication swap and the division undo are written down in the copybook step instead. Work through the four beams in order:

• 4 + 9 balances 9 + 4 — swapping the order in an addition keeps it level; ask what stayed the same.
• 6 + 3 balances 3 + 6 — same swap idea with different numbers, both pans make 9.
• 8 balances 14 − 6 — the right pan takes back the 6 that was added, landing right back on 8; one undoes the other.
• 15 balances 20 − 5 — the right pan takes the 5 back off the 20, landing on 15. Pause before this one and ask what has to happen to the 20 to bring it back level.

This round is for talking it through together — no marking yet. Pupils take turns at the board and the class agrees or corrects out loud. The beam presents the four tasks one at a time; slide the missing block until it levels, then hold out for the reason before pressing on.

For the two swap tasks the answer is the number that was swapped (6, then 5). For the two undo tasks the answer is the number you started with before you took away (7, then 9) — the subtraction hands the number back. One undoes the other — say it each time the beam settles.

This is the practice round — pupils solve on their own before the class checks together. Pupils take turns at the board, check each answer, and the class confirms before moving on. Keep the board work brisk rather than over-explaining.

The first two questions test the swap rule (answer 8, then 4); the last two test the undo rule with fresh facts (answer 6, then 8). On the undo questions ask what number went in before we took the block away, before revealing — this is where the undo idea has to do real work.