Claim-Evidence Writing
Overview
Practice writing CER statements about scientific models - defending model choices, explaining limitations, and justifying revisions.
Practice Problems
Question 1: Write a claim about why scientists use models.
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Answer: Example: "Scientists use models to represent complex systems that are too large, small, slow, fast, or dangerous to study directly."
A good claim is specific and can be supported with evidence.
Question 2: Provide evidence for this claim: "The Bohr model of the atom is useful for 8th grade chemistry."
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Answer: Example: "The Bohr model correctly predicts energy levels in hydrogen, explains electron configuration patterns used in bonding, and allows students to visualize abstract atomic structure."
Evidence should be specific and directly support the claim.
Question 3: Write reasoning connecting this claim and evidence. Claim: Computer models are essential for climate science. Evidence: Global climate involves millions of variables across decades.
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Answer: Example: "Because climate systems involve so many interacting variables over long time periods, it would be impossible to study them through direct experimentation. Computer models can simulate these complex interactions and project future scenarios based on different assumptions."
Reasoning explains WHY the evidence supports the claim using scientific principles.
Question 4: Write a CER defending this statement: "All models have limitations."
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Answer: Claim: All models have limitations. Evidence: The solar system model can't show accurate size AND distance; the Bohr model doesn't show electron clouds; weather models become inaccurate beyond 10 days. Reasoning: Models must simplify reality to be useful; any simplification necessarily leaves out some information. This trade-off between accuracy and usability is inherent to all models.
Complete CER connects all three parts logically.
Question 5: A model predicted 50 grams of product, but the experiment yielded 45 grams. Write a CER explaining the difference.
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Answer: Claim: The model overestimated product yield by not accounting for real-world factors. Evidence: The model predicted 50g but actual yield was 45g, a 10% difference. Reasoning: Theoretical models assume perfect conditions - 100% reaction completion, no side reactions, no loss during transfer. Real experiments lose some product to incomplete reactions and physical handling.
Scientific reasoning explains the gap between model and reality.
Question 6: Evaluate this CER: "Claim: Models are bad. Evidence: They aren't real. Reasoning: Only real things matter in science."
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Answer: Weak CER - Claim is too broad; Evidence doesn't support usefulness claim; Reasoning contradicts scientific practice where models are essential tools
Good CER requires nuanced claims, specific evidence, and reasoning based on scientific understanding.
Question 7: Write a claim about when a model should be revised.
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Answer: Example: "A model should be revised when new evidence consistently contradicts its predictions or when its limitations prevent it from explaining newly discovered phenomena."
This claim captures the key principle of model revision in science.
Question 8: Support with evidence: "Physical models are better than computer models for some purposes."
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Answer: Example: "Physical models allow hands-on manipulation that aids spatial understanding - studies show students learn DNA structure 20% better with physical models than diagrams. Physical models also don't require technology access and can be modified quickly during class discussion."
Evidence should be specific, ideally with data or concrete examples.
Question 9: Why is CER writing important for standardized science tests?
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Answer: SAT and ACT science sections require analyzing claims, evaluating whether evidence supports conclusions, and understanding scientific reasoning - exactly what CER practices
CER directly builds the analytical skills tested on standardized exams.
Question 10: Write a complete CER about models of your choice.
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Answer: Example: Claim: Food web models are more useful than food chains for understanding ecosystems. Evidence: Food chains show only one path (grass to rabbit to fox), while food webs show that foxes also eat mice and birds, and rabbits are also eaten by hawks. Reasoning: Ecosystems involve complex interconnections; if one species disappears, food webs show how energy can flow through alternative paths, while food chains would incorrectly suggest complete system collapse.
Practice writing complete CERs to build the skill automatically.