Rice Field Water Watch

Two identical trays. One in the sun, one in the shade. Mark both, check daily for a week.

This is a controlled comparison, which is a large idea arriving in a small package. Everything is the same except one thing, so the difference must come from that thing. Five year olds can follow this if the two trays are physically side by side at the start and separated only afterward.

The sun tray loses water noticeably faster and the result is reliable enough to build a lesson on.

The page has the setup, a daily marking chart for each tray, and the closing comparison. It also flags the mistake we made first time, which was two trays of different sizes. The comparison collapses and the children, correctly, do not believe the conclusion.