Walking Water Rainbow

Coloured water “walks” along paper-towel bridges into empty glasses and mixes there — a slow, visible chain of causes ending in a brand-new colour the child predicted.

  1. Stand 5 clear glasses or jars in a row. Half-fill glasses 1, 3 and 5 with water. Leave 2 and 4 empty.
  2. Let the child stir food colouring into the full ones: red in glass 1, yellow in glass 3, blue in glass 5.
  3. Fold 4 sheets of paper towel into long strips. Bridge each pair of neighbouring glasses with a strip, one end in each glass.
  4. Before anything happens, ask: “What do you think will happen to the paper? What will end up in the empty glasses? What colour?” Draw or write the child’s predictions.
  5. Watch for a few minutes as the colour climbs the paper, then go and do something else. Check back after 30 minutes, then after 2 hours.
  6. When the empty glasses have filled, ask: “Where did this water come from? Why is it green and not yellow or blue?”

Variation: run a comparison alongside — one pair of glasses joined by paper towel and one pair joined by a strip of plastic bag or foil. Ask why only one bridge worked.

Requirements

  • Space: A windowsill, counter or table that can be left undisturbed for a few hours
  • Surface: Flat and wipeable; a tray or old towel underneath catches drips
  • Materials: 5 clear glasses or jars, water, red/yellow/blue food colouring, paper towel, spoon, paper and crayons for predictions
  • Participants: 1 adult + 1 child
  • Supervision: Moderate during set-up; none needed while it runs

Rationale & Objective

“Understands that mixing colours produces a new colour” is a listed example for this subdomain, and here the mixing happens without anyone stirring — so the child has to reason back along a chain: the paper soaked up water, the water carried colour, two colours met, a new colour appeared. Following a cause through several steps and over a delay is harder than instant push-button effects and is a real stretch at five. Recording a prediction and comparing it with the result follows Head Start ELOF’s Scientific Reasoning goals and HighScope’s predicting and drawing conclusions indicators. UK Development Matters asks adults to help children “talk about the differences between materials and changes they notice,” and the foil-bridge comparison shows that the material of the bridge is what matters. Gelman & Brenneman (2004) argue that preschool science works best when children predict, observe and record around one connected idea rather than watching a one-off “magic” demo.

Progress Indicators

  • Early: fascinated by the colours but makes no prediction; on return says “it’s green” without linking it to the yellow and blue glasses
  • Developing: predicts that water will move or that the paper will get wet; afterwards says the green “came from” the neighbouring glasses with prompting
  • Proficient: predicts the new colour in at least one empty glass; explains the result as a sequence (“the paper sucked up the blue and the yellow and they mixed”)
  • Advanced: predicts both mixed colours and that the levels will even out; explains why the foil bridge failed; suggests own test (“what if the paper is longer?”)

Safety Notes

  • Food colouring stains clothes, wooden surfaces and grout — use a tray, old clothes and wipe drips promptly
  • Use sturdy glasses or plastic jars, placed where they cannot be knocked off by the child, siblings or pets
  • The coloured water is not for drinking; tip it away when the experiment ends
  • The wait is long for a five-year-old — set it up before another activity so the child is not asked to sit and watch

Hints

  • Playfulness: tell it as a story — the colours are neighbours who want to visit each other but have no bridge. Who will build one?
  • Sustain interest: take a photo at each check-in and flip through them like a slow film. Repeat another day with different colour pairs
  • Common mistake: filling the glasses too little or using long, thin strips — the water stalls and nothing mixes. Fill to three-quarters and keep the bridges short and thick
  • Limited space: use 3 small jars (two colours and one empty) on a windowsill
  • Cross-domain: draw the glasses before and after (visual arts); name the colours in order (vocabulary); compare water levels with a ruler or finger-widths (measurement)
  • Progression: two colours and one empty glass → full five-glass row → add a comparison bridge of another material → child plans a new version and predicts

Sources

  • Head Start ELOF — Scientific Reasoning (makes predictions; analyzes results, draws conclusions, and communicates results)
  • HighScope Science & Technology KDIs — Predicting, Drawing conclusions, Natural and physical world
  • UK Development Matters (2021), Understanding the World — “talk about the differences between materials and changes they notice”
  • Gelman, R. & Brenneman, K. (2004), “Science learning pathways for young children,” Early Childhood Research Quarterly, 19(1)
  • Worth, K. & Grollman, S. (2003), Worms, Shadows, and Whirlpools: Science in the Early Childhood Classroom
  • Singapore NEL — Discovery of the World