Claim, Evidence, Reasoning: Sentence Starters for Elementary Science Conclusions
By Ahmed, founder
“I learned that it was fun” is not a science conclusion. A real conclusion answers the question, backs the answer with numbers and explains why. The claim, evidence, reasoning (CER) frame gives students a simple structure to do exactly that.
The three parts
Claim: the answer to the question. One sentence.
Evidence: the data that supports the claim. Numbers from the experiment, with units.
Reasoning: the science that connects the evidence to the claim. Why did this happen?
A worked example
Imagine a student tested which material keeps an ice cube frozen longest.
- Claim: “The wool sock kept the ice frozen longest.”
- Evidence: “After 45 minutes, the ice in the sock had melted 12 mL of water. The ice in foil had melted 27 mL, and the unwrapped ice had melted 31 mL. I did this three times and the sock was best each time.”
- Reasoning: “Wool traps air, and air doesn’t pass heat on well. The sock slowed down the heat flowing from the room into the ice, so less melted.”
Notice how each part does a different job. The claim answers, the evidence proves, and the reasoning explains.
Sentence starters
Print these or put them on the board.
Claim
- I found that ______.
- My prediction was / was not correct because ______.
Evidence
- In my test, ______ measured ______, but ______ measured ______.
- The average for ______ was ______, which is ______ more than ______.
- In ______ out of ______ trials, ______.
Reasoning
- This happened because ______.
- This matters because ______.
- If I did this again, I would change ______ so that ______.
Teaching it by age
K to Grade 2: Use it orally. Ask, “What did you find out?” (claim), “How do you know?” (evidence), “Why do you think that happened?” (reasoning). An adult can write down the words. “I found out the sock kept the ice the longest, because I saw it still there when the others were water” is a real conclusion.
Grades 3 to 5: Students write each part in one to two sentences. Require at least one number in the evidence. Model a good and a weak example side by side.
Grades 6 to 8: Ask for multiple pieces of evidence, a graph, and reasoning that uses a scientific idea, such as particles or energy transfer. Add a sentence about what could make the result unreliable.
Common problems and fixes
- The claim just restates the question. Ask, “What’s the answer?”
- The evidence is a feeling. “It looked like more” becomes “It was 27 mL.”
- The reasoning is missing. Ask, “Why do you think that happened?” until they give a reason.
- The result didn’t match the prediction. Say that this is fine. “My prediction was wrong, and here’s what the data showed” is strong science.
Practise on other people’s claims
CER isn’t only for writing up your own experiment. Give students a claim from an advert, a website or even a chatbot and ask: What’s the evidence? Is it enough? Does the reasoning make sense? Our lessons How do you know a fact is true? and Which source should we trust? do this with experiments students can run in a class period. See also how to teach students to check AI science answers.
Where to find more
The free Science Fair Planner includes a CER page students can fill in. The fair-test planner helps with the step before. Our guide to teaching the scientific method covers the whole process, and you can sign up to download three lessons free.