When a child asks, “What will happen?”, an adult's first instinct is often to explain. Try something different today: do not reveal the answer—help the child test it.
Tomorrow, 10 November, is UNESCO's World Science Day for Peace and Development. It highlights the importance of science in society and in everyday life. Families do not need a laboratory to take part. A sheet of paper, a glass of water, two ice cubes or a toy car can become the beginning of genuine scientific thinking.
These seven challenges are not magic tricks with an explanation added at the end. Each one asks the child to follow the same five-step routine:
- Predict: What do you think will happen?
- Explain: Why do you think so?
- Test: Try it under clear conditions.
- Measure: Record what actually happened.
- Change: Alter one factor and test again.
That final step matters. A fair test changes one variable while keeping other conditions as similar as possible. The goal is not to guess correctly. The goal is to use evidence to improve an idea.
Begin with three family science rules
Keep every activity safe and enjoyable:
- An adult should supervise young children, scissors, small objects and spills.
- Do not taste experiment materials or use flames, sockets, medicines, chemicals or breakable containers.
- Stop if any material causes irritation, and wash hands and dry the work area afterwards.
Use coins or small counters only with children old enough not to place them in their mouth. Throw paper planes away from faces, people, animals and fragile objects.
Give the child a simple record sheet with five boxes: My prediction, What I changed, What I kept the same, My result, My next question. A notebook works perfectly.
Challenge 1: Build a stronger paper bridge
You need: Two equal-height books, two identical sheets of paper and coins or counters.
Place the books about 15 centimetres apart. Lay one sheet flat across them to form a bridge. Add coins one at a time near the centre and count how many it holds before collapsing.
Now give the child the second sheet. They may fold it, curve it or make a zigzag shape, but cannot add tape or another material. Test the redesigned bridge with the same books, gap and type of coins.
Ask before testing:
- Will folding the paper make it stronger?
- Which shape will carry the largest load?
- Where should each coin be placed for a fair comparison?
The variable to change: The shape of the paper.
Measure: The number of coins held.
Keep the same: Paper size, book spacing, coin type and coin position.
The important discovery is that material is not the only source of strength; shape affects how a load is distributed. If the redesigned bridge fails early, that is useful evidence. Ask what the child would change in version three.
Challenge 2: Run an ice-melting race
You need: Two similar ice cubes, two plates, half a teaspoon of salt and a timer.
Place one ice cube on each plate. Sprinkle the measured salt over one cube and leave the other untreated. Start the timer. Observe both cubes at one-minute intervals for five minutes.
Ask the child to predict which cube will produce more liquid water first. They can draw the cubes or measure the puddle approximately with a teaspoon at the end.
The variable to change: Salt or no salt.
Measure: Visible melting after the same amount of time.
Keep the same: Ice-cube size, plates, location, observation time and room conditions.
For another test, compare a small measured amount of salt with a larger amount—but use fresh, similar ice cubes. Do not change the salt quantity and cube size together, because then the result will not show which change mattered.
Afterwards, explain that dissolved salt lowers water's freezing point. Let the observation come before the explanation so the child has evidence to connect with the idea.
Challenge 3: Find the most absorbent paper
You need: Equal-sized pieces of two or three paper types, water, a teaspoon and separate plates.
Possible materials include a paper towel, tissue and ordinary writing paper. Place one equal-sized sample on each plate. Add one teaspoon of water to the centre of each and wait 30 seconds.
The child must decide how to measure absorption. One simple method is to lift each sheet carefully and observe how much water remains on the plate. Older children can add water one teaspoon at a time until a sheet begins to drip.
The variable to change: Type of paper.
Measure: Teaspoons held before dripping, or water left on the plate.
Keep the same: Sample size, water quantity, waiting time and placement.
Ask, “What would make this test more reliable?” The child might repeat each test three times and compare results. Repetition introduces an important scientific habit: one result may be affected by an uneven sheet, a measuring mistake or chance.
Challenge 4: Predict sink or float—and then improve the rule
You need: A bowl of water and five safe, water-resistant objects such as a plastic cap, metal spoon, wooden pencil, rubber eraser and small toy block.
Before touching the water, the child sorts each object into “sink” or “float” and writes a reason. Test the objects one at a time.
The most useful moment comes when a prediction fails. Ask the child to improve their rule. “Heavy things sink” will not always work: a large empty plastic container may float while a tiny metal object sinks. Material, shape, trapped air and how much water an object displaces all matter.
The variable to change: The object.
Measure: Whether it sinks, floats or remains partly submerged.
Keep the same: Water container, water level and how the object is placed.
Extend the challenge by shaping equal pieces of modelling clay into a compact ball and a hollow boat. Use only non-toxic reusable clay and do not put it in the mouth. Can the same amount of material behave differently when its shape changes?
Challenge 5: Make a shadow grow and shrink
You need: A torch or phone flashlight, a small opaque object, a wall and a ruler. Use the light only as a torch; do not stare into it.
In a dim room, place the object between the light and wall. First keep the object close to the wall, then move it closer to the light. Trace or measure the shadow height at three marked positions.
Ask:
- When will the shadow look largest?
- Does the object itself change size?
- What happens to the shadow's sharpness?
The variable to change: Distance between the object and light.
Measure: Shadow height.
Keep the same: Object, wall, light source and alignment.
Children often say a larger shadow means the object has grown. The measurements help separate appearance from physical change. Older students can draw straight lines from the light past the object's edges to model why the shadow changes.
Challenge 6: Test which surface slows a toy car
You need: A toy car, a firm board or large book for a ramp, books to support it, a ruler and two landing surfaces such as a smooth floor and a folded towel.
Build a low, stable ramp. Mark one release point and let the car go without pushing it. Measure how far it travels after leaving the ramp. Repeat three times on the smooth surface, then place the towel at the bottom and repeat.
The variable to change: Landing surface.
Measure: Distance travelled.
Keep the same: Car, ramp height, release point and release method.
Ask the child why pushing the car in one trial would make the comparison unfair. The activity makes friction visible and also demonstrates why repeated trials are better than relying on one exciting run.
For a second investigation, keep the surface unchanged and alter only the ramp height. The child should predict how this will affect distance before testing.
Challenge 7: Change one feature of a paper plane
You need: Two identical sheets of paper, tape for a floor starting line and a measuring tape. Adult supervision is needed if scissors are used, but cutting is not required.
Make two planes using the same basic design. Change only one feature on the second plane—for example, fold up small wing tips. Stand behind the same line and launch each plane with a similar gentle throw. Measure the distance and note whether the flight was straight, curved or unstable.
The variable to change: One wing feature.
Measure: Flight distance or time in the air.
Keep the same: Paper, basic design, starting line, room and thrower.
Human throwing is difficult to keep identical. Ask the child how this affects confidence in the result. Repeating several launches and using the median distance can reduce the effect of one unusually strong or weak throw.
This is a valuable lesson: real experiments are rarely perfect. Scientists identify limitations rather than pretending they do not exist.
What parents should say instead of giving the answer
The quality of the questions matters more than a long explanation. Try:
- “What do you notice?”
- “What evidence supports that idea?”
- “What changed between the two tests?”
- “Did we accidentally change anything else?”
- “How could we measure that?”
- “Would the result be the same if we repeated it?”
- “What will you try next?”
Avoid saying “That is wrong” when a prediction fails. Say, “Our result was different from the prediction. What did the test teach us?”
A wrong prediction followed by honest observation is better science than a lucky guess with no reasoning.
Turn one challenge into Olympiad practice
After completing an activity, ask the child to create one multiple-choice question about it. For the toy-car challenge, they might ask:
“Which change would make the test of floor surfaces unfair?”
A. Using the same car
B. Releasing from the same mark
C. Raising the ramp for the second surface
D. Repeating each test three times
The correct answer is C because two variables would change. Writing a question requires the child to identify the principle, plausible mistakes and evidence—skills that transfer to science Olympiads.
Celebrate the process, not the performance
At the end, do not ask only, “Did you get the right answer?” Ask:
- Which result surprised you?
- Which test was fairest?
- What mistake improved your method?
- What new question do you have?
Science grows through curiosity disciplined by evidence. A ten-minute challenge cannot teach an entire chapter, but it can build the habit behind every chapter: wonder, predict, test, measure and revise.
For World Science Day, the best gift may be resisting the urge to explain everything—and giving a child the time to discover something carefully.
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Frequently Asked Questions
What age are these science challenges suitable for?
With adult supervision, most challenges can be adapted for children aged approximately six and above. Younger children can predict and observe, while older students can measure, repeat trials, identify variables and explain limitations in greater detail.
What should a parent do when a child's science prediction is wrong?
Treat the unexpected result as useful evidence. Ask what happened, whether the test was fair and what the child would change next. Scientific thinking improves when children revise ideas from observations rather than trying only to protect a correct guess.
How do these home experiments support Olympiad preparation?
They develop observation, cause-and-effect reasoning, measurement, variable control and interpretation of evidence. Parents can extend each activity by asking the child to make a data table, explain the result and write a multiple-choice question based on the experiment.