Code: AC9M3N03 (partial). Goal: explain a three-digit addition by two physical exchanges, then check reasonableness. Prepare: H/T/O cards and large paper counters.
- Invite · 2. Ask whether
347 + 286is closer to 300, 600 or 900;350 + 280 ≈ 630gives a benchmark, not exact evidence. - Model · 5. Combine 7 and 6 ones → 13, exchange ten for one T. Combine 4 and 8 tens plus new one → 13 T, exchange ten for one H. Combine 3 and 2 H plus new one → 6 H. State
347 + 286 = 633, close to estimate. - Guided · 6. Learners direct
268 + 175: 8+5=13 ones, 6+7+1=14 tens, 2+1+1=4 hundreds; total 443. Reverse-check 443−175 if ready. - Choice · 6. Choose D18-A/B/C. Require a model or labelled exchange and a reasonable estimate, not just a final numeral.
- Exit · 4. Solve
156 + 278; expected 434. Ask where each exchange happened and why 334 is not enough. If a learner writes 334, recount hundreds after ten exchange. - Note · 2. Record model, accurate total and reasonableness separately; schedule a two-digit revisit if needed.
Access/home/extension: Pre-cut bundles, adult moves at direction, speech/AAC or number-line addition as an alternative. Do not time calculation speed as the only achievement. Extension: show a second correct partition of 347+286.