Look at these dry seeds. What do you think they need before they can grow into healthy plants?
Hands up one idea. We will turn one of your ideas into a real test today.
A fair test is a test where only one thing is different. We change one thing, we measure one thing, and we keep everything else the same.
Why does that matter? Think about a race. If one runner starts ten metres ahead, the race is not fair, and the winner does not tell us who is fastest. A science test works the same way. If two things are different at once, we cannot tell which one made the difference.
Plants need light, water, warmth, air and something to grow in. Let's think through one fair test together, about warmth: does cress grow better somewhere warm or somewhere cool? No group in this room will run this test. Listen for four things:
- the question
- the prediction, and the reason for it
- the one thing that changes
- the things that stay the same
Plant tests take days, so we will not know the answer this afternoon.
The one thing we change in a fair test is called the factor.
In your group, choose the one factor you will test. Most groups will test light or water.
Has your group got a different idea? You may test it instead if you can say yes to all three of these questions:
- Can we set it up today with our cress kit: seeds, cups, cotton wool or soil, water and dark card?
- Will it be the only thing that is different between our two cups?
- Is it safe?
Warmth was our worked example, so choose something else. Put up your hand and check your idea before you start.
Say your testable question out loud, then your prediction and why. Predictions are the start of the science, not a guess to get right.
Our question: Does … change how well our cress grows?
We predict … because …
You will see six cards on the board: amount of light, amount of water, how healthy the seedlings look, type of seed, amount of soil or cotton wool, and how warm or cool it is.
We sort them together for a test nobody in this room is running: a warm place against a cool one. Watch where each card lands, because the shape is the same whatever you change.
Then your group plans its own test on the Investigation Journal page. Write your question and your prediction at the top. Then fill in the plan: your one factor goes into Change. Work out what must stay the same.
What do plants need to grow?
Before anyone moves, we agree the places together: bright windowsill for light cups, dark cover or cupboard for dark cups, and one shared sill for the water-test cups and for any group testing its own idea.
Watch one labelled pair set up at the front first, so everyone sees matching amounts and a clear single-factor change.
Now set up the test your group planned.
Make your two cups the same in every way except the one factor you chose: the same number of seeds, the same amount of cotton wool and the same water. Label every cup clearly with your group name, the factor, and the condition (for example light or dark, full water or few drops).
Place your cups only in the places we just agreed.
Unlock the full learning experience
You're previewing this lesson. Get full access to this lesson and hundreds more — each one ready to teach, with interactive activities, printable resources and pupil progress tracking built in.
This lesson is copyright of Coding Ireland 2017 - 2026. Unauthorised use, copying or distribution is not allowed.