10 Days of Science with Math: How to Design a Fair Test


I know some of you are probably asking, “What is a fair test?” A fair test is when you conduct a experiment under fair conditions. To have fair conditions you need to make sure you only change one factor at a time while keeping all other conditions the same. Another way to look at it is to think about your outcome…when you finish the experiment you want to know that the results are based on just one factor (because that is the one you manipulated) not that it could be based on a few or you aren’t sure.

The first thing to do when considering an experiment is to make a prediction. Scientists call this a hypothesis and it’s easy to have your kids try it out. I like to use “I think ________ because _________.” statements. Not only do they make a prediction about the result of the test, but they have to tell you why.

Now it’s time to set up the fair test. First, you want a control- this is the item that remains unchanged in your experiment. Then you can choose one variable at a time to change. Variables are the changing factors in an experiment- to be a fair test only one can change each time you do the test. Remember, the factor you change is the one you are looking for in the experiment.

Let’s try out an example. A few years ago, my husband bought a whole bunch of gourmet popcorn and as we checked out all the varieties, my kids began to wonder which one would be the best. So, my husband and I (being the science people we are) suggested we find out- with that twinkle in our eye! We talked to the kids about how we’d find out and what would be the criteria for “the best”. Taste and the size of the popped corn came to mind. This led to the Great Popcorn Pop Off Extravaganza . In order to keep things fair, the popcorn had to be popped the same way. We measured out the weight of the kernels and the oil to be the same for all varities. These were the factors staying the same. Our changing variable was the type of popcorn since that is what we were testing for- which one of these would be the best. We didn’t want the results to be biased by using more oil with one type or using more kernels for another. The best tasting and biggest popcorn had to be the result of the type of popcorn alone. That is a fair test!

In summary, when doing an investigation/experiment:

  • change one variable
  • measure another variable
  • keep all other variables the same

Conducting a fair test is one of the most important ingredients of doing good, scientifically valuable experiments.

Now that you’ve done that fair test and you’ve collected data, it’s time to find out what you can do with it! And that is where the math comes in! Join me tomorrow when I discuss qualitative vs quantitative data- how to collect it and what to do with it.


Be sure to visit these brilliant women during our 10 days adventure between November 7th-18th! I love these ladies and we know you will too.

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