Codes: AC9M3N03, AC9M3A02. Target: explain 534 − 278 using place values or a checked number-line route. Set out: exchange cards, open number line.
- Frame · 2 min. Say: “If 278 is removed from 534, the answer must be smaller than 534. Roughly, 530 − 280 is 250.”
- Model · 5 min. Build 534. Exchange one ten for ten ones: 14 ones − 8 = 6. Exchange one hundred for ten tens: 12 tens − 7 = 5. Now 4 hundreds − 2 = 2. The remaining amount is 256; check with
256 + 278 = 534. - Second path · 6 min. Count up from 278: +22 to 300, +200 to 500, +34 to 534. Sum jumps
22 + 200 + 34 = 256. Ask why both paths solve the same missing-part question. - Partner attempts · 7 min. Choose 421 − 186 = 235 or 603 − 247 = 356. Partners show exchanges or count-up jumps, then verify by addition. Teacher listens for missing exchange or wrong total of jumps.
- Error repair · 3 min. Write an intentionally incomplete
534 − 278 = 344. Ask: “Could the ones be 4 when 4 − 8 needs an exchange?” Let children revise with pieces. - Brief check · 2 min. Everyone solves 302 − 157 = 145 or builds a count-up path 157→302. Focus learners state a check. If exchange across a zero is not yet secure, return to 302 with visible cards tomorrow.
Access: children can choose the equivalent number-line method; a scribe marks jumps they direct. Keep operation understanding separate from handwriting.