Designing a fair experiment

Ages 13 to 17 Read alone · about 55 minutes

Read together

A fair test changes one thing at a time. The thing you change is the independent variable. The thing you measure is the dependent variable. Everything else you keep the same: the controlled variables.

To trust a result, repeat it. One trial can be luck. Several trials let you find an average and see how much results vary. A bigger sample gives a better picture.

Science depends on honesty. Record what happened, not what you hoped. Report surprises. Other scientists should be able to repeat your work and check it. This is why results are shared and reviewed.

Do it

1. Choose a question you can test safely at home: “Which brand of paper towel absorbs the most water?” or “Does the temperature of water change how fast sugar dissolves?”.
2. Write your hypothesis, then name the independent, dependent and controlled variables. Plan exactly how you will measure.
3. Run at least five trials per condition. Record every result in a table, including odd ones.
4. Calculate the average for each condition and make a graph. Write a conclusion that states what the data show, and what limits your study.

Talk about it

• What would make this test unfair?
• What could go wrong with your measurements?

For the grown-up

Designing a fair test is the heart of the scientific method. Encourage honest reporting, even when results disappoint. Science is not only for experts, and families can practise it at home with safe materials.

Mark as done

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Where this comes from

• NGSS Lead States, Next Generation Science Standards (National Academies Press, 2013), Science and Engineering Practices: planning and carrying out investigations; analysing and interpreting data
• Karl R. Popper, The Logic of Scientific Discovery (Hutchinson, 1959)

Written with AI assistance and checked against the sources listed. Please read it before sharing it with a child.