Let students physically run the fair test and act out cause-and-effect chains.
Hands-on set-up, with roles
Make the seed planting a deliberate, tactile routine. Within each group, assign a Planter, a Measurer (owns the ruler), a Waterer (owns the measuring cup — the changed variable), and a Fairness Checker who confirms everything else is identical between pots. Students physically prepare two identical pots and change only the water.
Human cause-and-effect chain
Act out a drought or land-clearing chain. Students stand in a line, each holding a card (e.g. "less rain" → "soil dries" → "plants wilt" → "animals leave"). As you tap each, they step forward and say their link, physically walking the consequence down the line.