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What Is Claim-Evidence-Reasoning (CER)?

A practical teacher guide to Claim-Evidence-Reasoning: how claims, relevant evidence, and scientific reasoning work together in strong explanations.

Published and reviewed by STEMEngine AI · Updated August 2, 2026

Definition

Claim-Evidence-Reasoning (CER) is a scaffold for constructing scientific explanations and evidence-based arguments. A claim answers the question, evidence supplies relevant data or observations, and reasoning uses scientific principles to explain why the evidence supports the claim. CER makes the structure of explanation visible so teachers can diagnose whether a student is struggling with content knowledge, evidence selection, or logical connection.

Best used for

  • Explaining investigation results and scientific phenomena
  • Using data as evidence rather than merely reporting it
  • Assessing understanding of disciplinary core ideas
  • Supporting scientific writing and classroom argumentation

Core ideas

Claim

A clear, defensible answer to the scientific question. It should be specific enough to evaluate and should not merely repeat the prompt.

Evidence

Relevant observations, measurements, patterns, or credible information that support the claim. Strong evidence is specific and sufficient, not a list of every available fact.

Reasoning

The logical bridge connecting evidence to the claim through an accepted scientific principle, model, or mechanism. Reasoning answers: Why does this evidence matter?

Revision

CER is not only a final writing format. Students should revise claims when new evidence appears and strengthen reasoning through critique and discussion.

How to implement it

  1. 1

    Ask an evidence-bearing question

    The question must permit a defensible answer and give students access to observations, data, text, or a model they can use as evidence.

  2. 2

    Separate evidence from interpretation

    Have students identify what the data show before explaining why the pattern occurs.

  3. 3

    Name the scientific principle

    Reasoning should use the concept or mechanism that connects the evidence to the claim—not simply restate both.

  4. 4

    Compare and critique explanations

    Use peer review or whole-class analysis to test relevance, sufficiency, and logical coherence.

  5. 5

    Fade supports over time

    Begin with organizers, sentence frames, or partially worked examples; gradually remove them as students internalize the explanation structure.

Classroom example

Example: chemical or physical change?

Question: Did combining the two substances produce a chemical change?

  1. 1.Claim: combining the substances produced a chemical change.
  2. 2.Evidence: the temperature changed without external heating, gas bubbles formed, and a new solid appeared.
  3. 3.Reasoning: energy change and formation of substances with new observable properties indicate that particles rearranged into different substances.
  4. 4.Revision: compare whether each observation alone would be sufficient and identify alternative explanations to rule out.

Consolidation

Distinguish observations from inference, then evaluate which evidence is relevant and how the particle model provides the logical connection.

Common mistakes

Calling a summary “reasoning”

Repeating the claim and evidence does not explain the connection. Require a scientific principle or mechanism.

Accepting all data as evidence

Students need to select information that is relevant and sufficient. Irrelevant facts can weaken an explanation.

Using CER as a rigid paragraph formula

The scaffold supports thinking, not only formatting. Scientific explanations can vary in length and organization while retaining the three functions.

Assessing writing mechanics as science understanding

Evaluate the scientific accuracy and logic separately from grammar so language demands do not obscure conceptual evidence.

Frequently asked questions

What does CER stand for?

Claim, Evidence, and Reasoning.

What is the difference between evidence and reasoning?

Evidence is the relevant data or observation. Reasoning explains why that evidence supports the claim by applying a scientific principle, model, or mechanism.

Is CER only for science?

It is most closely associated with science education, but the structure can support evidence-based explanation in mathematics, engineering, social studies, and source analysis.

How can teachers support students who struggle with CER?

Use annotated examples, color coding, evidence-sorting tasks, oral rehearsal, sentence frames, and separate feedback on the claim, evidence selection, and reasoning. Fade those supports over time.

Sources and further reading

STEMEngine AI is an independent educational tool and is not affiliated with or endorsed by the referenced authors or organizations.

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