The seed trial: a first real experiment for young scientists
W4C Science · Biology · 4 min read · Evidence: established science; activity is classroom practice
Growing cress on cotton wool is an old classroom activity. Turned into a fair test, it teaches the most important idea in science: change one thing, keep everything else the same.
A seed holds a tiny plant and a store of food. It can wait in a packet for months because it is dry. Water and warmth wake it up; light matters once the first leaves appear. Children can discover each of these for themselves in five days.
Set up the trial
Each team chooses one condition to test: water, light or temperature.
They set up two cups, each with cotton wool and 10 cress seeds, identical except for that one condition. For example: one cup watered, one dry; or one on the windowsill, one in a light-proof box.
They label both cups and write a prediction.
Every day for five days, they count how many seeds have sprouted and write the number in a table.
On day five, children can draw a simple bar chart: two bars, one for each cup. Put all the teams' charts on the wall and compare.
The surprise
Seeds in the dark box usually do sprout, and the shoots come up long, thin and pale. This is a great moment. Most children predicted "no light, no growth". Ask them why the plant might grow tall in the dark. (It is stretching to find light, and it cannot make its green colour without it.)
Keep it fair and safe
Check the questions a scientist would ask: did both cups get the same seeds, the same amount of cotton wool, the same room? Were the seeds untreated? Ask families about allergies before handling soil or seeds, never let children eat any part of a plant used in class, and wash hands afterwards. These points come from the US National Science Teaching Association's primary safety guidance.
Try this tomorrow. Soak five beans overnight and leave five dry. In the morning, let children feel and compare them. Ask: what changed, and what do you think happens next?
Related resource: W4C-120 Young Scientists Lab has this trial as a full session, plus yeast, roots-and-shoots and habitat investigations. Coming soon to EduStore; subscribe to the newsletter to hear when it opens.
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