Primary Science Fair Tests: Explain What Changes and What Stays the Same

Begin with the question being investigated

A KiasuParents discussion about Science open-ended answers raises how and why questions about fair tests. For primary pupils, a useful answer needs to connect the test setup to the comparison being made. Writing that everything must be the same is incomplete, because one intended factor must change if the investigation is to compare its effects.

MOE’s Primary Science teaching and learning syllabus includes recognising and designing fair tests using changed and unchanged variables. Use the materials appropriate to your child’s cohort and current class topic. The example here is an original paper-based investigation to discuss at home; no special equipment or home experiment is needed.

Name the changed and measured variables

Imagine a diagram comparing toy cars released from ramps at different heights. The investigation asks how release height affects the distance a car travels along the floor after leaving the ramp. The changed variable is the release height. The measured outcome is distance travelled, using a consistent starting point for that measurement.

Ask your child to label these separately before writing a sentence. Distance is not kept constant here, because it is the outcome being investigated. Nor should the answer simply say that the ramp changes: the relevant feature is its release height. Specific labels make it easier to check whether the proposed method answers the question.

Explain relevant controls

For this comparison, use the same car, the same ramp and floor surface, and the same release procedure without an added push. These controls help reduce other explanations for a difference in distance. If one trial uses a heavier car and another uses a different surface, an observed difference cannot confidently be attributed to release height alone.

An answer should link a control to its purpose. For example, keeping the floor surface the same helps prevent differences in the surface from changing how far the car travels. This is more informative than a memorised statement that an unchanged variable simply makes the test fair. Choose controls relevant to the stated setup.

Distinguish fairness from repetition

Repeating each height can help show variation in the measurements and support a more dependable comparison. It does not automatically repair a biased setup. If one height always uses a different car, repeating both conditions many times leaves that additional difference in place.

Before discussing repeats, check that the intended comparison is fair. Then consider how readings would be recorded and compared. Follow the question’s instructions about averages or other treatment of the data. Do not invent a fixed number of repetitions that every school question supposedly requires.

Read a diagram as evidence

Cover the answer key and ask your child to find one feature that supports fairness and one that would weaken it. Then ask what result would be needed before describing a trend. Predicting that a greater height will produce a greater distance is different from reporting what actual observations show.

For a written correction, use three labels: change, measure and keep the same. Add one sentence explaining why a selected control matters. Revisit a different diagram later, since recognising the same idea in a new setup is a stronger check than memorising the toy-car example.

Choose a suitable practice question from our Primary Science papers, checking the level, year and original instructions.

Sources and further reading

Checked on 7 November 2026. The linked discussion is real; worked examples and practice routines are our original guidance. Older discussions are not evidence of current examination rules.

• Section B (open ended questions) for science — Exact post date unavailable in the accessible discussion excerpt.
• Official curriculum reference