For a full-blown experiment, kids use the fair test. They compare two (or more) things. All other variables are controlled. Asking students to measure and repeat seals the deal.
The Fair Test in Ms. Sneed’s Classroom
Our favorite fourth grade teacher sat at the side table with her mentor. “I’d like to do some experiments in my light unit,” she said.
“You mean you’d like to plan and carry out investigations,” Mrs. Brown said, pointing to a list of the NGSS science practices. She read aloud:
Plan and conduct an investigation collaboratively to produce data to serve as the basis for evidence, using fair tests in which variables are controlled and the number of trials considered.”
“Whew!” Ms. Sneed exclaimed. “What does that mean?”
Her mentor chuckled. “Basically, it means you use the scientific method. Flexibly, though. Kids use inquiry and compare only one variable at a time. Then they make generalizations. Let’s look a little more closely at this document.”
The two teachers studied the NGSS science practices more thoroughly. As they worked, Ms. Sneed said, “I see that kids should also answer testable questions, use measurement tools, make predictions, and observe. But the most important term seems to be “fair test.”
Four Factors in a Fair Test
“So,” Mrs. Brown asked, “how will you convey it to your students?”
Ms. Sneed picked up a pencil. On a blank sheet of paper, she jotted down four factors: compare, control variables, measure, and replicate. Then she explained each factor to her mentor:
- Compare – A fair test compares two or more things. This comparison is known as the variable (or independent variable).
- Control Variables – In a fair test, all other variables must be controlled. These variables are known as the controls (or controlled variables).
- Measure – In order to be fair, a test must include measurement with scientific tools. This can occur in set up and data collection.
- Replicate – Scientists do experiments over and over again. This ensures that their results are valid.
“Wow, great!” Mrs Brown exclaimed. “These four factors will help your students understand the difference between science activities and full-blown science experiments – and pass their standardized tests!”
Ms. Sneed Plans a Fair Test
Mrs. Brown sat back in her chair. “How will you improve a science activity?”
“Next week, I’d like my students to separate black ink into the colors on the visible spectrum. I absolutely love this chromatography experiment. Usually, I just have kids observe how black marker separates into colors of the rainbow. But this year, I’ll make some changes. Actually, I think it will work well with a fair test!”
Once again, Ms. Sneed picked up her pencil. “First, I’ll select an independent variable. Let’s see…” As she jotted down a list of possibilities, Mrs. Brown looked on.
- types of solvent
- types of paper
- colors of ink
- brands of markers
“I think I’ll try colors of ink,” Ms. Sneed said. “Additionally, I’d like to provide the question. How about ‘What color will separate into the most colors?'”
“Sounds good to me. What will you need?”
“As far as materials, I’ll need four plastic cups, four coffee filters, four markers, four pencils, and water for each lap group.”
“And a lab sheet,” said Mrs. Brown. She pulled out her laptop, and the two got busy. In no time, they’d whipped up a document that would reinforce the science processes Ms. Sneed wanted to emphasize.
Ms. Sneed Tells a Story
On the day of the chromatography experiment, Ms. Sneed was ready to introduce the fair test. “Today,” she said to her class, “I’d like to tell you about an experiment I conducted. I wanted to find out if a tomato plant grows more indoors or outdoors. I bought two tomato plants. One was a little bigger, but that’s okay, right? I put the bigger plant outside and kept the smaller one indoors. Whenever they got dry, I watered them. The bigger one got dry faster, so I watered it more often. At the end of two weeks, the outdoor plant has grown much wider. The indoor plant has grown taller. As a matter of fact, it’s growing toward the window. What can I learn from this experiment?”
Ms. Sneed’s students had a lot to say! Some thought the outdoor plant grew more; some said the indoor plant won. Then one small voice piped up, “How can we figure out which one won? You didn’t say how much each plant grew. Didn’t you measure them?” The other students nod in agreement.
“And what about the water?” asks another student. “You weren’t watering them the same.”
Introducing the Fair Test
“Ah, you are right,” Ms. Sneed confessed. “But I do have a solution to this problem. It’s called the fair test. A fair test allows us to compare one factor while keeping all others the same. The thing you’re testing is called the variable, or independent variable. You keep everything else exactly the same. All of these things that are the same are called controls, or controlled variables. You might also hear the term dependent variable. That’s what happens because of your independent variable – in other words, the result.”
Then Ms. Sneed asked her students to name the variables for the tomato experiment. As they discussed, she listed them on the board:
- independent variable – indoors or outdoors
- controlled variables – size of original plants, type of original plants, amount of soil, type of soil, containers, amount of water, temperature of water, how often they’re watered, etc.
- dependent variable – how tall or wide the plant grows (The class felt that they needed to choose one or the other. Therefore, they made the question more specific: “Does a tomato plant grow taller indoors or outdoors?”)
“How else can we be sure about our results?” Ms. Sneed asked. “How do I know that this will happen every time tomato plants are grown?”
A student in the back raised her hand. “I guess I’d try it again and see if the same thing happened.”
“Great job, everyone!” Ms. Sneed exclaimed. “Let’s make a list of steps that we’ll take to make a fair test in our class.”
After collaborating, the class had a list of four steps:
- Compare
- Control
- Measure
- Replicate
Conducting the Fair Test
“Is everyone ready to try a fair test?” asked Ms. Sneed. (Of course, they were!) She set out all of the materials and science equipment (including graduated cylinders and rulers). A student distributed the lab sheets. Then the science groups began working. And the experiment began!
Enjoy Teaching Science
Not every science activity works well with a fair test. But many do. If your students conduct even one full-blown experiment per month, they’ll become better scientists. Of course, you can use the fair test when addressing content standards. Or you can try some fun add-ons like this gummy bear experiment.
