Science Fenns K-5Grades K to 5
Two paper cups with bean seedlings, one in sun and one in a dark cupboard, with a ruler and a notebook beside them.

Science / All lessons / The Scientist’s Toolkit

Design an Experiment

Question, variable, controls, steps.

Lesson 3 of 41

Try this first

Before we start

Today’s story

Design an Experiment

Mia noticed her bean plant leaned toward the window. She wondered, does light change how fast it grows? Wondering is where an experiment starts.

A good experiment changes one thing and keeps the rest the same. The thing you change is the variable. The things you keep the same are the controls. Then you measure what happens.

You will write a question, make a prediction, plan the steps, and decide what to measure. Here is how.

See it

Five steps. Every time.

    Hands on

    Which Paper Towel Holds the Most Water?

    30 minutes · Do this with a grown-up nearby

    You need

    • Three brands of paper towel
    • Measuring cup
    • Water
    • Shallow pan
    • Notebook
    • Scissors

    Do this

    1. Write your question and your prediction.
    2. Cut each towel to the same size.
    3. Pour the same amount of water in the pan each time.
    4. Dip one towel for ten seconds and lift it out.
    5. Measure how much water is left in the pan. Subtract to find what the towel soaked up.
    6. Repeat for each brand, then run each one a second time.
    Write or draw: A table with brand, trial one, trial two and the average water absorbed.

    Watch for: Which things did you keep the same? Did the second try match the first?

    Safety: Wipe up spills right away so no one slips.

    Same every time

    Three rules

    Rule 1Change only one thing

    If two things change, you cannot tell which one mattered.

    Rule 2Measure with numbers

    Numbers are easier to compare than opinions.

    Rule 3Repeat the test

    One try can be luck. More tries give more trust.

    Grandpa Fenn’s notebook

    Say it like a scientist

    variable
    A thing in an experiment that can change.
    control
    A thing you keep the same in every test.
    prediction
    What you think will happen and why.
    hypothesis
    A testable idea about how something works.

    Poppy’s quiz

    Six questions

    Tap an answer. Green means right. You will see why.

    Talk about it

    Say it out loud

    • How do you know your test was fair?
    • What have you wondered about at home that you could test?
    Did you know

    Many great discoveries began with a wrong prediction that sent a scientist looking harder.

    Someone who does this

    A food scientist runs fair tests to find out which recipe stays fresh longest.

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