Teach & case
Help a near-peer reason through the idea — when you explain it, you understand it best — then read the real decision it comes from.
Help Hattie design the test
In a minute you'll be the teacher. Get ready to teach Hattie: a controlled experiment.
In a controlled experiment you change one variable and keep the rest the same, so you know what caused the result.
What you've shown you can teach
A case · you decide
Hattie's plant experiment
Hattie — a student testing whether a new fertilizer makes plants grow taller for a science fair
Hattie wants to prove her fertilizer works. Her plan: give the fertilized plant more sun and more water too, "to really give it the best chance." After two weeks it's taller — proof the fertilizer works?
The fertilized plant got MORE fertilizer, MORE sun, AND more water than the control. It grew taller — but which of the three caused it? The design can't say.
A controlled experiment changes ONE thing (the fertilizer) and keeps everything else — sun, water, soil, pot, seed type — identical between the two plants. Then any difference is attributable to the one variable.
Hattie's plant got more fertilizer, sun, AND water, and grew taller. Does that prove the fertilizer worked?
To fix it, what should differ between the fertilized plant and the control?
Hattie re-runs it: same sun, same water, only the fertilizer differs — across five plants each. That's Hattie's whole thing: change one variable, hold the rest, and let the result actually mean something.
When two ideas meet: 2 cases with two people
A case · you decide
Corvo and Fenn: the thing behind the link
Corvo & Fenn — a student who won’t call a link a cause, and a friend who hunts for the hidden variable
A town's data shows that on days with more ice-cream sales, there are also more swimming accidents.
Corvo refuses to say ice cream causes accidents. Fenn asks what else is different on those days.
What best explains the link?
Corvo held off. Fenn found the reason.
A case · you decide
Cal and Hattie: a test that can answer
Cal & Hattie — a student who controls variables, and a friend with a testable hunch
Hattie predicts a new fertiliser makes bean plants grow taller. She plans to put the fertilised pots on the sunny sill and the others in the hall.
Cal points out that sunlight also makes plants grow taller.
How should they set up the test?
Hattie's prediction became testable once Cal held everything else still.