Goal: recognise equal observed duration when start/stop are shared and withhold a duration claim from stop order alone when starts differ. Proposed code: AC9MFM01. Prepare: Card 119, Set G two-lane aids and separate START/STOP cards.
- Retrieve · 3 min. Child recalls how the class knew which action lasted longer in yesterday's start-together run.
- Model · 4 min. Start two actions together and stop together. State they lasted the same length of time in this run; no number of seconds needed.
- Guide · 5 min. Start A, start B later, stop A, then B. Point out that a later B stop alone does not settle which lasted longer.
- Independent try · 7 min. Give a fresh staggered-start demonstration; ask child what can and cannot be concluded. Child directs a reset with a shared START, then uses the stops to compare.
- Check · 4 min. A peer/adult offers “B was more fun, so it was longer.” Child gives one observed timing clue instead, without ranking preferences.
- Exit · 2 min. Child indicates a fair comparison setup. If they claim from staggered stop order, replay with clear distinct starts before Day 120.