Year 3 Science: Setting up a fair test
Part of the Year 3 Science working scientifically chapter. Chapter overview · whole chapter on one page
Setting up a fair test
A fair test is a test in which only one thing changes. We change the one thing we want to test. We measure what happens, and we keep everything else the same.
A comparative test compares the results for different things, such as three kinds of towel. If only the towel changes, the test is also a fair test.
A fair test helps us trust the answer. If we changed two things, we could not tell which one made the difference.
Key ideas
- In a fair test, only one thing changes.
- Measure the result of the change in the same way each time.
- Keep the other things the same: the size, the amount, the place and the way the test is done.
- If two things change, we cannot tell which one made the difference.
Method. Find the things that are different between the two tests.
- Read the material. The sponge and the cloth are different materials.material changes
- Read the size. The sponge is big and the cloth is small, so the size also changes.size changes too
- Write the answer. no
Check. Two things changed: the material and the size. ✓
Watch out. Use the same size of sponge and cloth, so that only the material changes.
Method. Find the thing that stays the same, then the thing that changes.
- Read the drop height. The drop height is 50 cm for every ball, so it stays the same.drop: 50 cm every time
- Find the thing that changes. The ball is different each time, so the ball changes.ball changes
- Write the answer. the ball
Check. The drop height stays at 50 cm. ✓
Method. Find the thing we change, and the things we keep the same.
- Read A. The kind of towel is the thing we change, so it does not stay the same.A: changes
- Read B and C. The amount of water and the pouring height are kept the same.B and C: same
- Write the answer. B and C
Check. Only the towel changes. ✓
Watch out
Watch out: a pupil who uses a bigger towel as well as a different kind of towel has changed two things. Check every thing before you start.
Try it at home or school (with a grown-up). Use three paper towels or kitchen cloths of the same size. Put a tray under each one. Pour the same amount of water (for example, 100 ml from a measuring jug) onto each one, from the same height. Compare how much water drips into the tray.
Exam tip
Grown-up tip. Ask your child: “What are we changing? What are we keeping the same?” Let them point to each thing as they name it.
Exercise 1B Fair tests and comparative tests
Method. Look for the thing that is different in each test.
- Read what we compare. We are comparing three towels.compare towels
- Find the thing that is different. Each test uses a different kind of towel.kind of towel
- Write the answer. the kind of paper towel
Check. The towel is the one thing that changes. ✓
Method. Think about the result we want to know.
- Think about the result. We want to know how much water did not soak into the towel.water in the tray
- Name the measurement. We measure the water that drips into the tray, in ml.ml in the tray
- Write the answer. the ml of water in the tray
Check. We measure the result, not the thing we change. ✓
Method. Check whether the amount of water stays the same.
- Read the amounts. One towel has 100 ml and the other has 50 ml.100 ml and 50 ml
- Decide. The amount of water changed, so the test is not fair.amount changed
- Write the answer. no
Check. The same amount of water must go on each towel. ✓
Method. Find the thing that we change.
- Find the thing we change. We change the kind of towel.kind of towel: changes
- Find the thing we keep the same. The size of the squares stays the same.size: same
- Write the answer. the size of the squares
Check. Only the kind of towel changes. ✓
Method. Think about what could change the bounce height besides the ball.
- Think about the test. The ball changes, so the other things must stay the same.ball changes
- Name one thing to keep. The drop height is one thing that must stay the same.drop height: same
- Write the answer. Accept any one of: the drop height, the table or the way the ball is dropped.
Check. Keep the same drop height, so that only the ball changes. ✓
Method. A comparative test compares results for different things.
- Read A. It compares two cups and what they hold.compares cups
- Read B. It asks for a personal view, so it is not a comparison.opinion
- Write the answer. A
Check. Two cups are compared with the same water. ✓
Method. Count how many things change.
- Count the changes. Three things change: the colour, the size and the weight.3 changes
- Decide. In a fair test only one thing changes.not fair
- Write the answer. no
Check. Change one thing only, and the test would be fair. ✓
Method. Think about the rule for a fair test.
- Think about the rule. Only one thing changes in a fair test.one thing
- Read the number. So the number of things that change is one.one
- Write the answer. 1
Check. One changed thing keeps the test fair. ✓
Method. Think about the rest of the test.
- Think about the rest. All the other things are kept the same.the same
- Check the rule. This is what makes the test fair.kept the same
- Write the answer. stay the same
Check. Keeping everything else the same makes the test fair. ✓
| Test | Towel | Water poured (ml) | Size of square (cm) |
|---|---|---|---|
| 1 | Cloth | 100 | 10 by 10 |
| 2 | Sponge | 100 | 10 by 10 |
| 3 | Cloth | 150 | 10 by 10 |
Method. Find the two tests where only one thing changes.
- Compare Test 1 and Test 2. The water (100 ml) and the size (10 by 10) are the same. Only the towel changes.only the towel
- Check Test 3. Test 3 has more water than Test 1, so two things change if we compare them with Test 1.water changes
- Write the answer. Tests 1 and 2
Check. Only the towel changes between Test 1 and Test 2. ✓
Method. Choose one thing to change, and keep the rest the same.
- Choose the thing to change. We want to compare balls, so the ball changes.the ball
- Keep the rest the same. The drop height and the table stay the same.drop height and table: same
- Write the answer. Accept any answer that names the ball as the thing that changes, such as “the ball”, because the drop height and the table stay the same.
Check. Only the ball changes in this plan. ✓
Method. Work out how much each towel soaked up. The biggest amount soaked up is the best towel.
- Work out the ml soaked up by each towel. Take the ml that dripped into the tray away from the 100 ml poured.A: 100 − 30 = 70; B: 100 − 12 = 88; C: 100 − 45 = 55
- Find the biggest amount. 88 ml is more than 70 ml and 55 ml.biggest: 88 ml
- Write the answer. Towel B
Check. Towel B soaked up 88 ml, the most of the three. ✓
Watch out. The number in the tray is not the amount soaked up. Take it away from 100 ml first.
Method. Count the things that changed, whatever their size.
- Count the changes. Two things changed: the towel and the pouring height.two changes
- Decide. When two things change we cannot tell which one made the difference, however small the changes are.not fair
- Write the answer. No. Accept any reason that says two things changed, so we cannot tell which one made the difference.
Check. Change only one thing for a fair test. ✓