---
title: "Fair testing"
description: "Set up simple comparative and fair tests, changing one thing on purpose and keeping other conditions that could affect the measurement the same"
canonical: https://lightmysky.com/learn/science/fair-testing-mt_qgb76wHN2X
source: https://lightmysky.com/learn/science/fair-testing-mt_qgb76wHN2X.md
retrieved: 2026-10-19
---

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# Fair testing

Set up simple comparative and fair tests, changing one thing on purpose and keeping other conditions that could affect the measurement the same

Subject: Science · Area: Scientific Inquiry · Ages 7 to 9
Page: https://lightmysky.com/learn/science/fair-testing-mt_qgb76wHN2X

## Ready when they can

- Explain what makes a test fair: change one thing on purpose and keep other things that could affect the measurement the same
- Identify the variable to change, the variable to measure, and the variables to keep the same
- Set up and carry out a comparative or fair test with support

## Lesson: Fair testing

A variable is something that can change. In a fair test, choose one thing to change on purpose. Decide what to measure. Keep other things that could affect that measurement the same. This helps you compare the effect of your chosen change.

**Example.** Mia compares soils for growing beans. She changes the soil type and measures plant height after two weeks. She keeps the bean type, pot size, water amount and light the same, and starts all the seeds at the same time.

*(drawing: After two weeks, one plant was 8 cm tall and the other was 4 cm tall. One comparison does not prove why they differed.)*

Plants can differ even in a fair test. Grow several beans in each soil and repeat the comparison. Record every height. Check whether the plants in one soil are usually taller.

If Mia changes both soil and water, she cannot tell whether a height difference is linked to soil, water or both. To compare soils fairly, she should give each pot the same amount of water.

**Example.** To compare two heights, subtract the shorter height from the taller height. Mia's plants were 8 cm and 4 cm tall. The difference is 8 minus 4, which is 4 cm.

**Recap.** Choose one change, measure the result, keep other relevant conditions the same, and repeat to check what you find.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Simple tests and experiments](https://lightmysky.com/learn/science/simple-tests-and-experiments-mt_Wa44s-f8Ws)

## Opens up

- [Drawing conclusions from evidence](https://lightmysky.com/learn/science/drawing-conclusions-from-evidence-mt_7VrR1GzhrN)
- [Controlling variables](https://lightmysky.com/learn/science/controlling-variables-mt_ArVBEpMAPk)
- [Fair testing (age 8+)](https://lightmysky.com/learn/science/fair-testing-age-8-mt_eoPcc4nrBE)