Making Predictions (Hypotheses) — Grade 3 Science

Remember how we practiced observations and turned them into scientific questions? Good — we’re using that detective work next.

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Hook: A tiny psychic? Nope — just science

Have you ever guessed which cookie will be gone first from the lunch table? That guess is a prediction. In science, a prediction that you can test is called a hypothesis. It’s like a smart guess with a plan to check if you were right.

What is a hypothesis (in kid-friendly words)

• Prediction: a guess about what will happen next.
• Hypothesis: a prediction that you can test with an experiment and that explains why you think it will happen.

Put simply: A hypothesis is a testable prediction with a reason.

Short example

• Prediction: "I think the plant will grow taller."
• Hypothesis: "I think the plant in sunlight will grow taller because it gets more light for food-making."

See the difference? The hypothesis tells which plant and why.

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How predictions connect to observations and questions

You already learned to observe carefully and ask good scientific questions. Now use those observations to make a hypothesis.

• Observation: "The seeds we put in the dark didn't sprout." (from Observations vs Inferences)
• Question: "Does light help seeds sprout?" (from Asking Scientific Questions)
• Hypothesis: "If seeds get sunlight, then they will sprout faster because sunlight helps plants make food."

That flow — observe → ask → predict/test — is the heart of scientific inquiry.

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How to write a good hypothesis (kid-tested steps)

1. Start with what you noticed (observation).
2. Turn it into a question: "What happens if…?"
3. Make a prediction that answers the question.
4. Give a reason (use what you already know).
5. Make it testable — can you check it with an experiment?

A helpful sentence starters:

• "I predict that ___ because ___ ."
• "If ___ (I do this), then ___ (this will happen), because ___ ."

Example sentence for Grade 3

"I predict that the ice cube on the sidewalk will melt faster than the ice cube in the shade because the sun directly warms the sidewalk."

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Classroom activity: Sink or Float Challenge

A quick, fun experiment you can do in class or at home.

Materials: small objects (rock, cork, coin, sponge, plastic spoon), a bowl of water, paper and pencil.

Steps:

1. Observe objects: look, feel, guess their weight.
2. Ask a question: "Which objects will sink and which will float?"
3. Make a hypothesis for each object using "I think... because..."
4. Test by placing each object in water and watching.
5. Record results and compare with your hypothesis.

Example hypotheses:

• "I think the rock will sink because it is heavy and solid."
• "I think the sponge will float at first because it has air inside, but it might sink if it gets full of water."

After testing, discuss why some guesses were right and why some were wrong. That’s science learning!

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Common mistakes (and how to fix them)

• Writing a guess with no reason: "I think the plant will grow." — add why: "because it gets light."
• Making a statement you can’t test: "Blue toys are better than red toys." — not testable in science class.
• Being too vague: "It will change." — change what? How?

Fix these by being specific (which thing?), adding a reason, and planning a way to test.

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Why hypotheses matter (even when they’re wrong)

• They help you plan a fair test.
• They make your thinking clear to others.
• A wrong hypothesis still helps you learn — it tells you what to change next time.

This is the moment where the concept finally clicks: a hypothesis is not a grade — it’s a tool. You use it to learn.

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Quick challenges (5–10 minutes each)

1. Weather prediction: Look outside. Make a hypothesis about tomorrow’s weather and tell why. "I predict it will rain because the sky is full of dark clouds."
2. Snack science: Which cracker will stay crunchy longer in milk? Hypothesize and test.
3. Shadow study: Predict how long your shadow will be at noon vs. late afternoon. Test and measure.

These small games build prediction muscles.

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How teachers (or parents) can check a student’s hypothesis

Ask these quick questions:

• Is the prediction clear? (Which object? What will happen?)
• Does it include a reason? (Because...)
• Can we test it with an experiment? (Yes/no)

If answer is yes to all three, great hypothesis!

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Key takeaways

• Prediction = a guess about the future.
• Hypothesis = a testable prediction that includes a reason.
• Use observation and scientific questions to make better hypotheses.
• Be specific, give a reason, and plan how to test it.

Final memorable line

Think of a hypothesis like a treasure map: it tells you where to look and why — and even if you don't find treasure, you discover something valuable.

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Try it now (one-minute practice)

Look around you. Pick one thing and make a hypothesis using this sentence: "I predict that _______ because _______." Say it out loud, write it down, or share with a friend.

Good scientists are always asking, predicting, and testing. Now go make a smart guess and see what happens!