Target/code: identify mass and directly compare two broad sealed same-size paper parcels using a stable adult-operated pan balance; AC9MFM01. Prepare: P169 2-sheet L/12-sheet H sealed envelopes, privately verified balance card.
- Notice · 3 min. Show the same-size parcels for a pretend shelter roof. Ask if looking at their outside tells which is heavier; mark any first impression as a guess.
- Model · 4 min. Adult places L and H on separate pans; show or neutrally describe which pan descends. Name the compared attribute mass, not parcel area.
- Guide · 5 min. Reset the balance. Child directs adult placement and identifies the lower pan; if the balance sticks, repair before continuing.
- Independent route · 7 min. Day 169 A/B/C uses actual verified parcels in toy shelter, model library delivery or theatre prop contexts. Child says H has greater mass because its pan went down, not because they know sheet counts.
- Reason check · 4 min. Swap parcels between pans. If the same parcel still tips downward, the evidence is stronger; if not, invalidate the device/materials and repeat later.
- Exit · 2 min. Child names the attribute and the observed comparison. No child lifts parcels; a neutral adult report can support access.