Sometimes it’s hard to emphasize the importance of having a fair test, when the experiments that students do are a little abstract and don’t seem to change even if they are sloppy in controlling variables.
This classroom demonstration of fair tests requires 2 tennis balls, a basketball, a blindfold and a bin or bucket (empty).
This classroom demonstration clearly teaches the importance of fair tests and will have students calling out “it’s not fair!”.
Ask for a volunteer. Tell the class you want to see who is better at throwing a ball in the bin – you or the student.
Give the student a tennis ball and have them stand about 5m away from a bin or bucket. Take the basketball and stand next to them.
Ask the class who they think will get the ball in. (But it’s not fair!)
You’re a reasonable teacher – you understand you had an unfair advantage with a larger ball. Concede defeat and take a tennis ball, but stand 1m away from the bin.
Ask the class who will be the better shot now. (But it’s not fair!)
Fine, you say, the ball size has to be kept the same and the distance from the bin has to be kept the same. Let’s make this a fair test.
Move to stand next to the student, but blindfold them.
It’s fair, you say. We’re the same distance away, we have the same ball. (It’s not fair!)
OK, you admit. It’s not fair. I’ll take the blindfold off. Now is it fair? (Hopefully, yes!)
This is a reminder to keep the way you measure (the distance from the bin), the equipment you use (size of ball) and the conditions (blindfolded or not) of the experiment the same to be a fair test. Only change one variable and aim to keep all others controlled or the same.
Thanks to the creative Mr Culley for this teaching strategy.