Fair testing

Set up simple practical enquiries, comparative tests, and fair tests, understanding the importance of changing only one variable at a time

ages 7 to 98 practice questionsvideo included

What a learner can do afterwards

Explain what makes a test 'fair' (only one variable changes, everything else stays 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

The lesson

A fair test is when you change only one thing and keep everything else exactly the same. The one thing you change is called the variable. If only the variable changes, you can trust that it caused the result you see.

Try it together

Mia wants to find out which soil grows the tallest bean plant. She changes the soil (that is what she changes). She measures how tall each plant grows (that is what she measures). She keeps the pot size, the water, and the sunlight the same for every plant (those stay the same).

After two weeks, the garden soil plant grew taller than the sandy soil plant. Only the soil was different, so the soil made the difference.

Good to know

If you change two things at once, like the soil and the water, you won't know which one caused the change. Change just one thing at a time.

A fair test changes one thing, measures one thing, and keeps everything else the same.

Watch it

Where it sits

Learn first

Simple tests and experiments

This opens up

Drawing conclusions from evidence Controlling variables

Where this leads

Jobs that lean on this skill. Follow one to see everything it is built on.

Astronaut Botanist Chemist Doctor Ecologist Epidemiologist

Then practise

8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.