Claim-Evidence Writing
Overview
Master the CER (Claim-Evidence-Reasoning) framework for scientific writing. This skill is essential for lab reports, scientific explanations, and standardized tests.
Practice Problems
Question 1: What are the three parts of a CER statement?
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Answer: Claim (answer/conclusion), Evidence (data/observations), Reasoning (explains why evidence supports claim)
CER connects the "what" (claim) to the "how I know" (evidence) to the "why it matters" (reasoning).
Question 2: Identify the claim: "The treatment plant grew taller because it received 20 cm average height compared to the control's 12 cm."
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Answer: "The treatment plant grew taller"
The claim is the main assertion or conclusion. It's what you're trying to prove or explain.
Question 3: What makes good scientific evidence?
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Answer: Specific data, measurements, or observations from experiments or reliable sources
"The plants grew more" is weak. "The experimental group averaged 20.3 cm vs. 12.1 cm for control" is strong.
Question 4: Write the reasoning for this CER: Claim: Fertilizer increased plant growth. Evidence: Fertilized plants averaged 25 cm; unfertilized averaged 15 cm.
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Answer: Example: "Fertilizer provides essential nutrients like nitrogen, phosphorus, and potassium that plants need for cellular growth and photosynthesis, explaining the 67% greater height in fertilized plants."
Reasoning uses scientific principles to explain WHY the evidence supports the claim.
Question 5: Identify what's missing: "Salt water freezes at a lower temperature. This is because salt interferes with ice crystal formation."
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Answer: Missing evidence - needs specific data
Complete version: "Salt water freezes at a lower temperature. In our experiment, fresh water froze at 0C while 10% salt water didn't freeze until -6C. This is because..."
Question 6: Why is "Because I think so" not acceptable reasoning in scientific writing?
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Answer: Reasoning must be based on scientific principles, not personal opinion
Science requires reasoning grounded in accepted knowledge, theories, or logical connections to evidence.
Question 7: Convert to CER format: "The ball bounced higher when dropped from a greater height."
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Answer: Claim: Ball bounce height increases with drop height. Evidence: Dropped from 50 cm, bounce = 30 cm; from 100 cm, bounce = 58 cm. Reasoning: Greater drop height means more potential energy, which converts to more kinetic energy, resulting in higher bounces.
Adding specific data and scientific reasoning transforms a simple statement into a CER.
Question 8: A student's evidence contradicts their claim. What should they do?
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Answer: Revise the claim to match the evidence, not the other way around
Scientific integrity requires conclusions that follow from data. Never change data to fit your expected conclusion.
Question 9: Rate this CER: "Plants need light to grow. My plant grew. Light is important for photosynthesis."
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Answer: Weak - vague claim, irrelevant evidence, reasoning doesn't connect to evidence
The evidence doesn't show light's role. Better: Compare plants with and without light, then explain photosynthesis connection.
Question 10: How does CER writing prepare you for standardized science tests?
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Answer: SAT/ACT science sections require analyzing claims, evaluating evidence, and assessing reasoning in passages and data
CER skills help you identify strong vs. weak arguments, connect data to conclusions, and write supported responses.