PTC NSWHomeGEMSPlanningStep 11: Variable Selection

Step 11: Selecting a Focus Variable

During the first mentor visit, students need to identify the variables in their fair test investigation.

How well students perform in this step will depend on the quality of their preparation and understanding of the activities in scaffolded investigations.

There are three types of variables that students must be aware of when conducting a fair test investigation. They are the dependent variable, control variables and the independent variable:

  • Dependent variable
    • The factor that is to be measured
  • Control variables
    • The factors that are to be kept the same
  • Independent variable
    • The factor that is deliberately changed in order to determine how it impacts on the dependent factor


Students who are new to the idea of fair testing may misunderstand the concept of what is to be measured – the dependent variable. For instance, if one of the control variables (those factors that are kept the same) entails measurement e.g. each cup contains 50 ml of liquid, then students may report that this is what they are measuring. If students have misunderstandings in this area they will need your assistance for clarification.

At this stage it may be useful to review change, measure and keep the same and steps in the scientific process.

Cows  Classroom-poster Conducting-investigations  Steps in scientific process 

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