A predict-then-test water investigation. The child guesses whether each of several household objects will sink or float, then drops them into a basin and compares the prediction to what really happened.
- Half-fill a clear basin or large bowl with room-temperature water on a towel-protected surface. Gather 6–10 small objects with mixed outcomes — a coin, a cork, a metal spoon, a plastic lid, a marble, a wooden block, a leaf, a grape, a crayon, a small candle, a rubber duck.
- Lay a simple two-column “Predict / What Happened” chart with the object names or simple icons. Give the child stickers in two colors — one for sink (down arrow), one for float (up arrow).
- Hold up the first object. Ask: “Do you think it will sink or float? Why?” The child places a sticker in the Predict column.
- The child drops the object in gently (no splashing) and observes. Place a sticker in the What Happened column.
- After all objects, count together: “How many did we get right? Were there any surprises?” Re-test the surprises to confirm.
Variation: test the same object in different forms — does an empty jar float? With the lid on? With a stone inside? Does Plasticine float as a flat boat but sink as a ball? These “same material, different shape” tests are where deeper reasoning develops.
Requirements
- Space: A table, floor, or bathtub with a towel under the basin
- Surface: Waterproof / wipeable; lay a bath towel down to catch splashes
- Materials: Clear basin or large bowl, room-temperature water 5–8 cm deep, 6–10 small objects of varied density, a two-column prediction chart on paper, stickers or two-color crayons, a hand towel
- Participants: 1 adult + 1 child; also works well with 2 children taking turns
- Supervision: Close — even shallow water is a drowning hazard for young children; never leave the child unsupervised at the basin
Rationale & Objective
The sink-or-float investigation is the canonical preschool inquiry activity (Worth & Grollman Worms, Shadows, and Whirlpools; Boston Children’s Museum STEM Sprouts; HighScope Science & Technology curriculum). Hsin & Wu (2011) showed that predict-then-test sequences with scaffolded talk produce significantly stronger buoyancy reasoning than direct instruction. Kloos, Fisher & Van Orden (2010) found that 5-year-olds reliably refine their density theories when given hands-on contrast trials with surprising counter-examples. The activity exercises the full inquiry cycle — predict → test → observe → compare → refine — and produces the productive surprises that drive conceptual change.
Progress Indicators
- Early: predicts based on the last object (“this will float because the other one floated”) or always picks one outcome; doesn’t compare prediction to result; loses interest after 2–3 items
- Developing: predicts based on a single feature (usually size); notices when a prediction was wrong but doesn’t revise theory; describes outcomes with simple words (“down,” “up”)
- Proficient: predicts based on multiple features (heavy + small vs. big + light); spontaneously says “I was wrong, I thought it would sink” and tries to explain why; engages with 6–10 objects in one sitting
- Advanced: forms and tests a rule (“things with air inside float”); designs follow-up tests (“what if I poke holes in the lid?”); records observations with drawings; remembers and applies findings days later
Safety Notes
- Even shallow water is a drowning hazard for under-5s — stay within arm’s reach the entire session and never step away “for just a second”
- Avoid items smaller than 4.5 cm across — they fail the CPSC small-parts cylinder test and are choking hazards if mouthed
- Skip rusty metal, sharp items (push pins, broken plastic), and anything that releases dye, paint, or detergent into the water
- Wipe up splashes immediately — wet floors are slip hazards
- Some “absorbent” items (sponges, paper) grow mold within days — discard or fully dry before reuse
- Watch for water in the eyes — keep a hand towel within reach and demonstrate a gentle drop, not a throw
Hints
- Playfulness: frame the basin as the “prediction pool” or “science pond.” A paper apron or homemade “Lab Pass” badge marks the activity as serious work, which 5-year-olds love
- Sustain interest: rotate the object set across sessions — kitchen day, bathroom day, garage day, nature-finds day. Keep a running “All-Time Surprise List” of objects whose result was unexpected
- Common mistake: the adult announces the answer (“that’s heavy, it’ll sink”) before the child predicts. Always ask the child first — the prediction is the inquiry. Using only same-density items (all plastic toys) also removes the surprises that drive learning; deliberately include counter-intuitive items
- Limited space: a salad bowl in the kitchen sink is enough. Five objects in 10 minutes is a complete session
- Cross-domain: count and compare (“3 sank, 5 floated” — numeracy); describe textures and shapes (vocabulary); sort objects into two piles after testing (classification); draw the basin with each object in its place (graphic representation)
- Progression: clearly different objects (cork vs. coin) → mixed materials (plastic toy with metal parts) → same object in different forms (foil ball vs. flat foil) → adding salt to water and retesting → testing what makes a boat (Plasticine ball that sinks, formed into a bowl that floats)
Sources
- Worth, K. & Grollman, S. (2003). *Worms, Shadows, and Whirlpools: Science in the Early Childhood Classroom*. Heinemann / NAEYC
- Hsin, C.-T. & Wu, H.-K. (2011). "Using scaffolding strategies to promote young children's scientific understanding of floating and sinking." Journal of Science Education and Technology
- Kloos, H., Fisher, A. & Van Orden, G. (2010). "Preschoolers' reasoning about density: Will it float?" Child Development
- Boston Children's Museum, National Grid & WGBH (2013). *STEM Sprouts Science, Technology, Engineering & Math Teaching Guide*
- Gelman, R., Brenneman, K., Macdonald, G. & Roman, M. (2009). *Preschool Pathways to Science (PrePS)*. Brookes Publishing
- HighScope KDIs — Observing, Experimenting, Predicting, Drawing conclusions (Science & Technology content area)
- Head Start ELOF — Scientific Reasoning sub-domain (P-SCI 1, 5, 6)
- Teaching Strategies GOLD Objective 24 (scientific inquiry) and Objective 26 (physical properties)
- NSTA / NAEYC Joint Position Statement on Early Childhood Science Education (2014)
- UK EYFS — Understanding the World (The Natural World ELG)