Does Repeating an Experiment Make It a Fair Test? | Bukit Timah Science Tuition Guide

Did you know that repeating the same unfair comparison does not remove the extra factor that made it unfair? In a simple school investigation testing one factor, keep other relevant conditions comparable. Repetition can help show how consistent the measurements are; it does not by itself isolate the intended cause.

For Bukit Timah parents checking Science tuition work, ask two different questions: “Was the comparison designed to test this factor?” and “Were the measurements repeated?” A child who answers both with “repeat three times” may be applying a memorised phrase without checking what the investigation needs.

Keep the diagram and the child’s first explanation. Ask the tutor to contrast a fair comparison with a repeated but confounded one. Then give a fresh setup and ask which change would repair the design. This makes the next learning step clearer than adding repetitions automatically.

In a simple controlled comparison, an investigator changes the factor being tested, measures a specified outcome and keeps other relevant conditions comparable. If another relevant factor also differs, it becomes harder to attribute the outcome to the intended factor.

Repeated measurements can reveal variation and help assess consistency. A consistently biased measurement or a consistently confounded design can still give misleading evidence. The word “repeat” is therefore not a universal repair.

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Suppose a worksheet asks whether water amount affects plant growth. Plant A receives more water and is placed in strong light. Plant B receives less water and is placed in shade. Even if Plant A grows more, both water and light differ.

Repeating those two treatment combinations with more plants would not separate the effect of water from the effect of light. A repair for this simple comparison is to use comparable light conditions while varying water amount, with other relevant conditions considered too.

The specified growth measurement, starting conditions and observation period also matter. A fairer design improves the comparison; it does not guarantee a particular result.

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If the child writes “repeat the experiment”, ask what changes in the setup after repeating. If water and light still vary together, the attribution problem remains. Encourage the child to name the extra factor and say how it should be controlled.

Then ask why repeats may still be useful after the design is improved. Individual plants can vary, and measurements can fluctuate. A student who can explain both purposes is reasoning beyond the stock phrase.

Use a paper-based teaching illustration rather than prescribing an unsupervised practical experiment. Any real investigation should follow the school’s instructions and suitable supervision.

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There is no single number of repeats that automatically makes every experiment valid. Follow the investigation instructions, the taught course and the purpose of collecting more data. Avoid inventing a universal examination rule such as “three trials always earns the mark”.

Older students may encounter designs that deliberately vary several factors. Those require methods that can distinguish their effects. The beginner’s controlled-comparison rule applies to the simple question being taught, rather than every form of scientific research.

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Keep a record headed “What else changed?” beside another headed “How consistent were the readings?” Ask the tutor which problem occurs in the actual question. The answers can lead to different practice tasks.

The 3-pax Mathematics reference shows why close inspection of reasoning matters. Use that principle when evaluating Science teaching, and confirm subject availability separately. Progress here is the child choosing a relevant repair and explaining what it improves.

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Continue with the closest question

• Fair-test variables or Science answering techniques
• Separate an observation from its explanation
• Separate aim, results and conclusion
• Bukit Timah tuition decision guide
• Bukit Timah tuition hub
• eduKateSG’s 3-pax Mathematics teaching guide

Match support to the actual course

Use the student’s current teaching coverage and examination-year syllabus. PG1–PG3 are Posting Groups; G1–G3 describe subject levels. See MOE’s Posting Groups guide and SEAB’s SEC information.

Reviewed 11 October 2026. Examples are original teaching illustrations; home checks are suggestions to discuss with the teacher or tutor.

Arrange a parent–student consultation after the starting position is clear. Bring the task, first attempt and the point where help was needed.