The Vanishing Puddle

An outdoor investigation of where water goes: the child chalks around a puddle, comes back later, and works out what made it shrink — and why the shady one is still there.

  1. On a dry, bright day pour two cupfuls of water onto paving to make two puddles of about the same size — one in full sun, one in deep shade. (After rain, use real puddles.)
  2. The child draws a chalk line around the edge of each puddle.
  3. Ask: “What do you think will happen to these puddles? Will they both do the same thing?”
  4. Come back every 15–20 minutes. Each time, draw a new chalk line around what is left, so the puddle gains rings like a tree.
  5. When the sunny puddle has shrunk or gone, compare: “Which one got smaller faster? What is different about where they are? So what made the water go?”
  6. Ask the harder one: “Where did the water go?” Accept the child’s idea, then offer yours — it went into the air in bits too tiny to see.
  7. Check it another way: make two wet handprints on the paving, one in sun and one in shade, and count how long each lasts.

Variation: on a breezy day, fan one wet handprint with a piece of cardboard and leave the other alone — does wind make water vanish faster too?

Requirements

  • Space: A patio, pavement, balcony or driveway with both a sunny and a shady patch
  • Surface: Hard paving or concrete (water soaks into soil, which spoils the test)
  • Materials: Cup or jug of water, chalk, optional timer and cardboard for fanning
  • Participants: 1 adult + 1 child; easy with several children
  • Supervision: Light — the adult brings the child back for check-ins

Rationale & Objective

Evaporation is a perfect cause-and-effect puzzle because the effect is obvious and the cause is invisible, so the child must reason from a comparison rather than simply watch. Two puddles that differ only in sun or shade make the cause identifiable, and the chalk rings turn a slow change into something a five-year-old can see and describe. This is the NGSS kindergarten expectation to “make observations to determine the effect of sunlight on Earth’s surface” and the EYFS Natural World goal of understanding “changing states of matter.” Piaget (1930) found that young children often give magical or purpose-based accounts of natural events; repeated evidence plus one plain explanation is how those ideas gradually shift. Returning to check a prediction and reporting the result exercises Head Start ELOF’s Scientific Reasoning goals, and Worth & Grollman (2003) describe water investigations like this as core early-childhood physical science.

Progress Indicators

  • Early: enjoys chalking and splashing; notices the puddle is “gone” but offers no cause, or a magical one (“someone drank it”)
  • Developing: predicts the puddle will get smaller; notices the sunny one shrank faster; says “the sun did it” with prompting
  • Proficient: explains the difference between the puddles unprompted (“it dried faster because the sun made it warm”); predicts the handprint result correctly
  • Advanced: applies the idea elsewhere (washing on the line, wet hair, a damp towel on the radiator); tests wind as a second cause; uses or asks about the word “evaporate”

Safety Notes

  • Use sun protection — hat, sunscreen and shade breaks — since the best days for this are bright ones
  • Wet paving is slippery; keep running feet away from the puddles
  • Stay well away from roads and driveways in use; a back patio or balcony is ideal
  • Paving in direct summer sun can be hot enough to hurt bare hands and feet — test it with your own hand before the handprint step
  • Standing rainwater puddles can be dirty; wash hands afterwards

Hints

  • Playfulness: the child is a detective on “The Case of the Missing Puddle” — the chalk rings are the evidence, and sun and wind are the suspects
  • Sustain interest: paint with water and a big brush on a sunny wall or fence and race to finish a picture before the first part disappears
  • Common mistake: giving the explanation before the comparison is finished. Let the two puddles do the persuading, then add the word “evaporated”
  • Limited space: indoors, wipe two wet stripes on a chalkboard or dark tile — one near a sunny window or warm radiator, one in a cool corner
  • Cross-domain: time each check-in with a kitchen timer (time concepts); count the chalk rings (numeracy); link to why we hang washing out (daily living)
  • Progression: watch one puddle shrink → compare sun and shade → predict before testing → add wind as a second cause → child designs a test for a new idea (big versus small puddle, warm versus cold water)

Sources

  • NGSS K-PS3-1 — make observations to determine the effect of sunlight on Earth’s surface
  • UK EYFS Understanding the World — The Natural World ELG (“important processes and changes in the natural world around them, including the seasons and changing states of matter”)
  • Head Start ELOF — Scientific Reasoning (makes predictions; analyzes results and draws conclusions)
  • Piaget, J. (1930), The Child’s Conception of Physical Causality
  • Worth, K. & Grollman, S. (2003), Worms, Shadows, and Whirlpools: Science in the Early Childhood Classroom
  • HighScope Science & Technology KDIs — Observing, Predicting, Natural and physical world
  • Finland ECEC — Exploring and Interacting with My Environment