Your child says an experiment is a fair test because both set-ups use a ramp. But one uses a different toy car as well as a higher ramp. If the cars travel different distances, which change explains the difference?
That is the useful question behind a fair test. For a simple comparison, deliberately change one factor, measure the outcome and keep other relevant conditions consistent. Saying “to make it fair” is a start; explaining what must stay the same shows more of the thinking.
This guide is for parents reviewing Science with their child. The toy-car task below is an original paper exercise, not an official examination question or a report of a real experiment. There is no equipment to set up.
Start with the question being investigated
Before choosing a pair of set-ups, write the aim in one sentence:
How does the height of the top of a ramp affect the distance a toy car travels along the floor after leaving the ramp?
That sentence gives us two jobs: change the ramp height and measure the distance along the floor. It does not ask which toy car is best or how quickly the car moves.
NASA JPL's experiment-planning guidance recommends forming a testable question and considering other factors that could affect the result. Our example applies that general advice; it is not a NASA activity or a Singapore marking scheme.
Give each variable a clear job
Ask your child to complete these three lines before looking for an answer:
- I will change: the height of the top of the ramp above the floor.
- I will measure: the distance the car travels along the floor, from the bottom of the ramp until it stops.
- I will keep the same: the toy car, ramp surface and length, floor surface, and way the car is released.
For this plan, the car starts from the same marked position at the top of the same ramp and is released without a push. Raising that ramp changes its slope as part of changing its height. We would not separately swap the ramp for one with a different surface.
The words “same car” matter more than “same colour”. Two cars can look alike but have different wheels or masses. Use the information given, and do not assume two objects are identical just because a drawing looks similar.
Which two set-ups answer the question?
In this invented plan, R and S are different toy cars. All three set-ups use the same ramp, floor surface and release method described above.
| Set-up | Toy car | Ramp height |
|---|---|---|
| A | R | 10 cm |
| B | S | 20 cm |
| C | R | 20 cm |
Pause here. Which pair would you choose to investigate ramp height? Explain your choice before opening the answer.
Show the comparison answer
A and C. They use the same car, R, while the ramp height changes from 10 cm to 20 cm. The other stated conditions remain the same.
A and B change both car and ramp height. B and C keep the height at 20 cm but change the car, so they address a different question. Using all three does not make A and B a fair height comparison.
Name the condition, then explain why
Try moving from a short label to a specific explanation:
Use the same toy car in both set-ups. A different car could travel a different distance for reasons other than the ramp height.
This explains why that condition matters to this investigation. It is more useful than listing every object in the picture. If a question requests one condition, choose one relevant condition and explain it clearly rather than adding unrelated details.
Punggol View Primary School's 2021 parent workshop makes the same general distinction: one changed variable, other relevant variables kept constant, and an explanation of how they could affect the experiment. We cite its fair-test guidance, not its dated assessment arrangements. Follow your child's current teacher and question wording.
Check the measurement as carefully as the set-ups
In this exercise, “distance” means distance along the floor after the car leaves the ramp. Measuring from the top of the ramp in one trial and from the bottom in another would give two different meanings to the recorded number.
A clearer plan states the same starting line, the same point on the car used for the reading, and the unit, such as centimetres. It also says that the reading is taken when the car stops. Ask your child to add those details in their own words.
The table contains a plan, so it cannot tell us which set-up actually produced the greatest distance. A prediction is not a measured result. Once results are supplied, our guide to using numbers in Science answers offers a separate practice task.
A short check for the next worksheet
Try three questions together: What are we finding out? What changes between the chosen set-ups? What exactly will be measured? Then ask for one relevant condition to keep the same and a reason.
If your child can name variables but cannot choose a pair, return to the aim and compare the table one column at a time. Keep the attempted answer to discuss with their teacher if the same difficulty continues. You can also explore Science support at Genie and arrange a free trial through the form below.