A guess is a quick idea with nothing behind it. A hypothesis is a guess that has grown up: it has a reason ("because I noticed...") and a way to test it ("we could find out by..."). Kids usually get it fastest in "If... then..." form: "If I water the plant, then it will grow!"
An example you can use at the table
Put a jar of something countable in front of your child, like pasta shapes or buttons.
- A guess: "I think there are a hundred."
- A hypothesis: "The jar looks about as big as the cup we filled yesterday, and that held about fifty. So I think about fifty. We could count one layer and check."
Both are numbers. Only the second has a reason and a plan. That is the whole difference, and your child can hear it.
How Chapter 3 teaches it
Chapter 3, The Great Guess, covers pages 26 to 40, and the title is a little joke: the "little thesis" is the great guess your child learns to make. A few pages to color together:
- Page 27, The Crystal Ball: "A hypothesis is a smart guess about the future."
- Page 28, If... Then... Machine: one chute says IF (water), the other says THEN (flower). This is the if-then pattern as a machine.
- Page 31, The Scale: a feather and a rock. "We make a guess, then we test it." Your child colors them to show which is heavier.
- Page 40, Locking it In: Subby locks the hypothesis in a safe before the testing starts.
Turning a guess into a hypothesis
When your child says "I think...", ask two follow-up questions:
- "Why do you think that?" This finds the reason.
- "How could we find out?" This finds the test.
You don't have to use the word "hypothesis" every time. "Smart guess" works fine for a four-year-old. Older kids often enjoy the real word once they see what it means.
For a longer explanation, including how if-then thinking shows up in reading and friendships, read The Difference Between a Guess and a Hypothesis.