Designing a Fair Test

Using the situation of fair competition, introduce students to concepts of the necessary elements of a fair test.

• CONTROLLING variables: making sure the only thing that changes in your test is what you plan on measuring.
• MULTIPLE trials: making sure that you don’t base your thinking on too few events.
• OBJECTIVE measurement: making sure that you measure using a system that others can use in the same way.

CONTROLLING variables: making sure the only thing that changes in your test is what you plan on measuring.

MULTIPLE trials: making sure that you don’t base your thinking on too few events.

OBJECTIVE measurement: making sure that you measure using a system that others can use in the same way.

Use Gregory’s complaints about the unfair running race to demonstrate the elements of a fair test.

Ask students if they can think of other ideas for addressing Gregory’s complaints.

Paraphrase:

Gregory thought that the contest to determine the best runner wasn’t a fair test. What kind of things could you do in a race to make sure that it fairly determined a winner?

Students now think about other ways that a race can be unfair and then remedy the problem using a principle of fair testing.

Sample answers:

• Nobody is making the runners all begin at the same place.
• Making it fairer: have a fixed start and finish line for competitors (objective measurement).
• The running course was wet in the morning and dry in the afternoon, and the winner had the best overall time of the day.
• Making it fairer: the competition can only occur on a day when the course is dry in both the morning and the afternoon (control of variables).

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Now students apply their understanding of the principles of fair tests to new situations.

Review the three principles for conducting fair tests. Read the first situation to the class.

Sample responses:

• Julio – Controlling variables. In order to to know which plant grows the fastest, Julio must control variables by using the same type of soil.
• Susan – Multiple trials and controlling variables. Susan doesn’t know if the sunny weather on a Tuesday had an impact on the sales of ice cream. In order to make that determination, she would need to sell ice cream on multiple Tuesdays to see if there is a pattern in the increased sales. Additionally, Susan needs to control the variables and compare the sales on sunny days to cool days.
• Tony – Multiple trials. In order for Tony to determine which boats are the fastest, Tony needs to consider multiple trials of the race because this single race could have been the first time that the German boats performed so well.
• Leah – Controlling variables. In order to determine which ball bounces the highest, Leah must pay more attention to controlling variables by not applying force to the tennis ball.
• Jackson – Objective measurement. Jackson should include objective measurements in his determination of the best brand of paper towels. For example, he should measure how much liquid the towels soak up.

This final response provides an additional formative assessment before students begin the lab.

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