Whoever said, “If you always do what you always did, then you will always get what you always got,” must have been a scientist. In the lab, sometimes getting the same result is desired. However, scientists frequently change one or more aspects to study its effect on the outcome. Every day, we consider variables without realizing it. How much flour will make the pie crust flakier? How will the weather affect the curing time of concrete?
Focus on the Process
Experimentation is a natural part of human curiosity, but before children can begin to understand how to manipulate experiments, they must understand independent and dependent variables. While teaching this concept can be a challenge, it is one that is imbedded in the other lessons of scientific inquiry. The focus should remain on the process rather than the outcome.
To begin, have learners consider a topic with which they already have experience - cause and effect. At the most basic level, independent variables are the cause and dependent variables are the effect. The class can illustrate mini posters to connect the relationship:
- If you talk on your cell phone too much, your bill will be higher.
- If your dog eats too much candy, he will get sick.
Identifying Variables in Fake Experiments
Once students feel comfortable with this, introduce them to scientific variables through mock experiments. The Great Fakesperiment was published by Science Scope in February 2009 and is still available online in various forms. There are ten stations that suggest a fake experiment followed by questions about the variables in a multiple choice format:
Meg and Mike want to grow the biggest watermelon possible to win the blue ribbon at the fair. Meg thinks that the watermelons will grow best in potting soil. Mike thinks they will grow best in sandy soil. They plant their seeds in the same sunny location, water them the same amounts, and wait.
- What is the independent variable?
- What is the dependent variable?
- What is the controlled variable?
Shawn Pelletier, a teacher in Berlin, Connecticut exposed his science classes to several of these exercises. He and his colleague found that the students’ ability to identify the independent variables increased from sixty-nine percent to ninety percent while the ability to identify the dependent variable increased from forty percent to eighty-three percent in a four week period.1
Taking Charge of Experimental Design
When learners are performing reliably with this type of exercise, have them construct very simple experiments based on a hypothesis you pose. For example: The farther a ball drops, the higher it will bounce.
They should design an investigation to test the idea and then:
- Explain what exactly will be measured and how it will be measured.
- Explain what exactly will be changed each time the experiment is conducted and how it is changed.
- Identify the independent and dependent variables.
Later, you can have your class design an investigation in which there might be more than one independent variable. The pendulum experiment is a good one for this because young scientists can test both the length of the pendulum and the weight of the bob. First demonstrate how a pendulum’s arc can be used to measure time. Then, ask the class if it might be possible to change the period, or the time it takes to make one trip. First, provide just balls of yarn, or twine, and similar-sized washers. Later, ask them if there are any other variables that might affect the outcomes. Be clear that they will need to explain what they changed and how it affected the length of the period.
Practice Makes Perfect
It is difficult for children to grasp a concept such as independent and dependent variables without lots of practice. Provide many opportunities for them to master this skill. As students design their own investigations, their understanding will deepen because they will have to justify the reasons for the outcomes achieved.
1Pelletier, Shawn, “Cracking the Method,” Science Scope, March 2009, 74-77.
Other ideas for teaching variables can be found on Lesson Planet:
Sixth through eighth graders explore variables as they study crater formation. The lesson incorporates several steps of the inquiry approach to experimentation. Allow at least three class periods.
Guide to Science Experiments
If you do not have time to find The Great Fakesperiment mentioned in the article above, this lesson provides four scenarios and asks learners to identify all pieces of the experiment, including the hypothesis, variables, and error analysis. I like it because students must examine data tables for some of the answers. The experiments are also applicable to a child’s world and worded in the way that most pupils would write an experimental design.
The Bouncing Ball
This can be adapted to many grade levels. Young experimenters test ways to affect the rebound of a tennis ball. Variables to consider may include height from which the ball is dropped, the type of ball, and the type of floor. To increase the amount of inquiry in the lesson, allow learners to design their own tests and come up with their own variables. Allow plenty of time for discussion of the results and what factors may have affected those results.