Controlling variables (age 11+)
Form a testable scientific hypothesis linking an independent variable to a predicted outcome, plan a full investigation identifying independent, dependent, and control variables, sample size, and risk assessment
What a learner can do afterwards
- Writes a hypothesis in the form 'I predict that [IV] will affect [DV] because...' supported by scientific reasoning
- Identifies and labels the independent variable, dependent variable, and at least three control variables
- Plans repeat readings and an appropriate sample size, and identifies relevant hazards with control measures
The lesson
A hypothesis is a prediction with a reason. Scientists write it like this: 'I predict that [the thing I change] will affect [the thing I measure], because...' The 'because' part explains the science behind your idea, not just what you think will happen.
Priya wonders whether water temperature affects how fast sugar dissolves. Her hypothesis: 'I predict that increasing the water temperature will speed up how quickly sugar dissolves, because heat makes the water particles move faster and bump into the sugar more often.'
Before testing, plan three things. The independent variable is what you deliberately change (water temperature). The dependent variable is what you measure (time to dissolve). The control variables are everything else you keep exactly the same, for example the amount of sugar, the amount of water, and how much you stir. Repeat each reading at least three times so one odd result doesn't spoil your data.
Always think about safety before you start. Hot water can scald, so list it as a hazard and write a control measure next to it, such as using oven gloves or asking an adult to pour it.
A strong investigation starts with a hypothesis that has a reason, then a fair test that changes only one thing, repeats its readings, and plans for safety.
Watch it
Where it sits
This opens up
Where this leads
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.