Claim-Evidence Writing
Learn
Scientific writing requires you to make claims and support them with evidence. This lesson teaches you the CER framework: Claim, Evidence, and Reasoning. This skill is essential for both scientific communication and standardized tests like the ACT Science section.
The CER Framework
- Claim: A statement that answers a scientific question
- Evidence: Data or observations that support your claim
- Reasoning: Explanation of how the evidence supports the claim using scientific principles
Examples
Work through these examples to see the concepts in action.
Example 1: Identifying Elements
Claim: The unknown sample is sodium.
Evidence: When placed in a flame, the sample produced a bright yellow color.
Reasoning: Each element has a unique emission spectrum due to its electron configuration. Sodium is known to produce yellow light when its electrons are excited, matching our observation.
Example 2: Periodic Trends
Claim: Atomic radius decreases across a period from left to right.
Evidence: Li has radius 152 pm, Be has 112 pm, B has 85 pm, C has 77 pm.
Reasoning: As protons increase, nuclear charge pulls electrons closer, reducing atomic radius while electron shells remain the same.
✏️ Practice
Test your understanding with these practice questions.
Practice Questions
0/3 correctWhat is the scientific method's first step?
A hypothesis is:
Which is a property of matter?
Check Your Understanding
Test yourself with these 10 quiz questions.
Question 1: What is the purpose of a claim in scientific writing?
Answer: A claim is a statement that directly answers a scientific question or makes an assertion that can be supported with evidence.
Question 2: What counts as valid scientific evidence?
Answer: Valid scientific evidence includes measurable data, observations, or results from experiments that can be verified and repeated.
Question 3: What is the role of reasoning in a CER response?
Answer: Reasoning connects the evidence to the claim by explaining the scientific principles that show why the evidence supports the claim.
Question 4: Why is it important to use specific numbers in evidence?
Answer: Specific numbers make evidence more credible, precise, and verifiable, strengthening the argument.
Question 5: What makes a weak claim in science?
Answer: A weak claim is vague, not testable, or not directly answering the question asked.
Question 6: How should you handle evidence that contradicts your claim?
Answer: You should address it by either revising your claim to fit all evidence or explaining why the contradictory evidence may be flawed or an outlier.
Question 7: What scientific principle would you use in reasoning about atomic radius trends?
Answer: Effective nuclear charge - the net positive charge experienced by electrons, which increases across a period as protons increase.
Question 8: How is CER writing similar to what scientists do?
Answer: Scientists make hypotheses (claims), collect data (evidence), and explain their findings using scientific theory (reasoning) in the same way.
Question 9: What is the difference between evidence and reasoning?
Answer: Evidence is the data or observations (what you saw/measured), while reasoning is the explanation of why that evidence supports your claim using scientific concepts.
Question 10: How can you strengthen your reasoning?
Answer: Reference specific scientific laws, theories, or principles; explain cause and effect; and connect multiple pieces of evidence logically.
Next Steps
- Review any concepts that felt challenging
- Move on to the Unit Checkpoint
- Return to practice problems periodically for review