Teaching Variables in Science

Instructor: Jill Burns

Jill has over 10 years experience teaching Earth Systems Science, introductory chemistry, and environmental science. She has earned a Master of Arts in Secondary Education.

This lesson will introduce teachers to how they can provide contextual clues to help students differentiate between independent, dependent, and controlled variables in a science lesson.

Variables in Science

'But isn't the independent variable and the control the same thing? I mean, the scientist is changing both of them. Aren't they?' Sound familiar? If so, you've come to the right lesson! Our students can struggle at times with common science vocabulary...even if it has been reiterated year after year. For those particular students, we need to provide simple ways to connect to these challenging words so we don't end up hearing 'This is too hard!' or 'I'm never going to remember this!' Let's explore how we can make the vocabulary words do the work for us in differentiating between scientific variables.

Mnemonic Devices

Controlled Variables (aka the control) are variables where no changes are, or will be, made in an experiment. This is the baseline of the experiment. Your students will compare all results to this particular set up during the analysis of their results. Let's say for example, you want your students to study how varying amounts of water influence the germination rate of radish seeds. Your controlled variables in this particular case will be the type of soil used, the amount of soil in each pot, the source of water, the type of seed, the amount of light exposure, the temperature, etc. These variables will remain constant for all experimental set ups so you know the variable you are testing is the only one influencing the rate of germination. So how do you get the idea of what controlled variables are to stick? I tell my students to look at the word controlled...it starts with c-o-n just like the word constant does. Controlled variables stay constant! It's also helpful to emphasize the con in con-trol and con-stant for your auditory learners when introducing (or reiterating) this variable in a lesson or lab.

Independent Variables are what the scientist is choosing to manipulate in the experiment to see how things will change. This is typically only one thing in an experiment that will be altered by the scientist. Why? If there are more than one independent variable, how does the scientist know what is causing the change? In the case of our radish seed germination example, the students would change how much water each radish seed set up will receive to see if/how varying amounts of water influence the rate of germination. Unfortunately, this is the variable that I've found to cause problems with some students. They think that because the scientist is changing this variable, it is then the controlled variable. What to do? I like to simply use the word independent, and point out that the letter I in independent means that I the scientist change this variable.

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