How to Teach Sink and Float in Kindergarten
Teach sink and float by asking children to predict what an object will do, test it in water and record what they actually observe. Begin with a few large, safe objects rather than a crowded collection. Keep the container, water level and waiting time consistent so children can compare results.
For kindergarten and Grade 1, the central learning goal is to distinguish “I think it will…” from “I saw it…”. A prediction that does not match the result creates a useful discussion. Children do not need to use density formulas or write full sentences to take part.
In this guide
Set a clear observation goal
Show a large wood block, a smooth stone and a metal spoon. Explain that each object will have its own test. Ask children to describe the objects before guessing what they will do in water.
Agree on practical meanings. “Floating” means an object remains at the surface without being held up. “Sinking” means it moves down through the water; note whether it reaches the bottom. An object can float with much of its body underwater. If an object changes position while you watch, record the sequence rather than forcing one immediate label.
Materials and adult preparation
Gather:
- A stable, shallow plastic tray with cool water deep enough to distinguish the surface from the bottom for your objects.
- One large wood block, one smooth stone and one metal spoon, all too large to swallow and without sharp edges.
- Towels and a separate tray for wet objects.
- Paper and crayons, or a simple prediction-and-observation chart.
- An optional orange for a later adult-led comparison, subject to your setting's food and allergy rules.
Adults should check the objects, run a preparation trial and supervise the water continuously. Keep water away from electrical equipment and wipe spills promptly. Do not use glass, tiny objects or tasting. Empty the water tray after the activity.
Select a small number of objects so everyone can see each test. The aim is to investigate these objects under these conditions, not to teach that every wooden, stone or metal object behaves identically.
A five-step sink-and-float investigation
1. Make a prediction before testing
Hold up one object. Ask, “What do you think this will do when we place it in the water?” Invite a reason, such as its material or a previous experience.
Record the prediction before the object touches the water. Children can point to a surface or bottom picture, draw a symbol or dictate an answer. Keep the prediction visible even when the test produces a different result.
2. Place one object gently in the water
An adult or closely supported child places the object without throwing it, pushing it down or holding it up. Let the water settle. Use the same agreed waiting time for each test; a short adult count can help the group watch together.
Ask, “Where is the object now?” before asking why. Look from the side when possible so an object resting below the surface is easier to locate.
3. Record an observation separately
Use a second column for what happened. A child may say, “I thought the spoon would stay up, but I saw it move to the bottom.” Preserve both statements.
| Object | My prediction | What I observed |
|---|---|---|
| Wood block | Child's own idea | Child's own observation |
| Smooth stone | Child's own idea | Child's own observation |
| Metal spoon | Child's own idea | Child's own observation |
Avoid filling the observation column in advance. Even familiar materials deserve an actual test, and an unusual result should lead to checking the setup rather than changing the child's record to match a worksheet.
4. Repeat one test
Choose an object and repeat the test with the same container, water level and waiting time. Remove other objects first. Ask, “Did we notice the same thing?”
If the result differs, look for a changed condition: was the object placed differently, was air trapped, or did it absorb water? Children can report the difference without needing to settle every possible explanation.
5. Make one evidence-based statement
Ask children to complete “In our test, the ___ floated/sank. I know because ___.” Accept a gesture toward the surface or bottom as part of the explanation.
Compare the claim with the observation chart. Praise noticing and checking rather than predicting correctly. Save the chart so children can use it when they later design boats.
Why “heavy things sink” is an unreliable rule
Floating involves an upward force from the water and the object's weight. The upward buoyant force equals the weight of water displaced by the submerged part of the object. A large ship and a small spoon show why size or heaviness alone is not enough to predict the result. NASA's explanation of Archimedes' principle provides teacher background.
For children, say, “Water pushes up. We need to test the whole object, including its material and shape.” Keep the explanation connected to the objects they can see.
Optional extension: test the same orange before and after peeling
First check food rules and prepare the orange yourself. Test one intact orange, record its position and remove it. An adult then removes the peel while keeping the fruit together. Retest that same orange using the same water setup. Observe the removed peel separately if appropriate.
Ask, “What changed? What stayed the same?” Do not promise that the orange will switch from floating to sinking. Fruit varies, and a peeled orange may remain afloat or float at a different level.
This comparison changes several physical features at once, including the amount of material, volume and structure of the orange. It can prompt questions about the peel, but it does not isolate one cause or prove an explanation by itself. Write down what happened to this orange.
Common questions about teaching sink and float
What if children change their prediction after seeing the result?
Keep the original prediction and add a new observation. Explain that changing an idea after gathering evidence is useful; erasing the first idea makes the learning harder to see.
What if an object floats and later sinks?
Record both events and the time or sequence you observed. You might write, “At first it stayed at the surface. Later it moved down.” Plan a separate investigation if children want to explore water absorption or another possible explanation.
Is this suitable for younger preschoolers?
With closer adult support, younger children can watch two large objects, point to their positions and tell what they noticed. The related teaching resource is intended for kindergarten and Grade 1; simplify the activity rather than assuming every page suits younger learners.
Optional slides and worksheets
The paid English Sink or Float Investigations — Science Slides and Worksheets supports prediction, repeated testing and an orange comparison. It provides PDF and PPTX materials; teachers supply the real objects, water tray and adult supervision. The PDFs are not fillable.
Use your own chart if you prefer. When children can distinguish a prediction from an observation, the Boat STEM Challenge offers a next question: “Can changing our design change what happens in the water?”
