Goal: compare mass with a checked balance rather than size inference. Proposed code: AC9MFM01. Prepare: Card 133, preflight Set M1 (equal trays, two versus five identical large blocks), approved balance.
- Question · 3 min. Ask “Which tray is heavier?” while both appear the same size. Avoid revealing hidden block count.
- Model · 4 min. Check empty equal trays balance; show how a side going down under the same conditions indicates more mass in that loaded tray.
- Guide · 5 min. Place loaded trays on balance without telling answer. Child watches/feels/hears agreed neutral indication and names what was directly observed.
- Independent compare · 7 min. Child repeats with positions swapped, names heavier tray relative to the other and shows the side/result. Offer child-directed adult handling.
- Check · 4 min. Reveal identical block counts only after first observation; ask whether size of container alone proved weight. Record if the balance malfunctioned and reprepare.
- Exit · 2 min. Child completes “I know because the checked balance ___.” If “looks bigger,” use Set M2 next.