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Science Practice Lab

Experimental design · Grades 5–8

Science Experiment Mistake Finder

Help students identify problems in experiments, evaluate fair tests, and explain how scientific investigations can be improved.

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Science Practice Lab

Find the Experiment Mistake

Name:
Date:

Read each experiment carefully. Find the mistake and explain how to fix it.

Scenario

Two groups of bean plants are grown to test how sunlight affects plant growth. Group A receives four hours of sunlight and 100 mL of water each day. Group B receives eight hours of sunlight and 200 mL of water each day.

1

Identify one problem with this experiment. Explain how you would fix it.

Scenario

A student rolls one toy car down a low ramp and one down a high ramp. She tests each ramp only once, then concludes that higher ramps always make cars roll farther.

2

Why is this conclusion not well supported? What should the student do?

What is an experiment mistake?

An experiment mistake is any problem in how an investigation is planned or carried out that makes its results less trustworthy. Examples include changing too many things at once, measuring carelessly, or drawing a conclusion the data does not support.

What makes an experiment a fair test?

In a fair test, only the independent variable changes. Everything else — the controlled variables — stays the same, so any difference in the results can be linked to the one factor that changed.

Common scientific experiment mistakes

These are the mistakes students meet most often:

  • Changing more than one variable at a time
  • Comparing groups that started out different
  • Using inconsistent or imprecise measurements
  • Running only one trial
  • Drawing conclusions the data does not show

How to use these worksheets in class

Use one scenario as a warm-up, ask pairs to compare their fixes, or assign a full worksheet before students plan their own investigation.

Examples

Uncontrolled variable

Testing two fertilizers, but one plant sits by a window and the other in a dark corner.

Measurement error

Timing a race with a stopwatch for one runner and by counting seconds out loud for another.

Unsupported conclusion

Testing one brand of paper towel and concluding it is the most absorbent of all brands.

Questions About This Tool

Continue learning

What Makes a Fair Test in Science?Common Science Experiment Mistakes (and How to Fix Them)

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Identifying Variables Practice

Practice recognizing independent, dependent, and controlled variables through real science scenarios.

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