How to Write Claim, Evidence, Reasoning (CER)

The claim answers the question or states the conclusion. Evidence is the relevant information used to support that conclusion, such as observations, measurements, patterns, results, or source-based facts allowed by the task. Reasoning is the justification that explains why the evidence supports the claim through scientific ideas, principles, mechanisms, or relationships.

These categories are connected but not interchangeable. 'The plant near the lamp grew taller' may be evidence if it reports an observation. 'The lamp caused more growth' is a claim about the relationship. Reasoning would have to explain why the measured pattern supports that conclusion and address whether the investigation actually controlled other important conditions. Labeling the jobs separately makes those distinctions easier to inspect.

A claim should be clear enough to evaluate. If the question asks which material is the best insulator in an investigation, the claim identifies the material supported by the results. It does not need to repeat every measurement or explain the mechanism yet. When the question asks for a relationship, the claim should state that relationship at the level the evidence can support.

Treat the claim as revisable. Scientific explanations are not stronger because a student refuses to change an early answer. If the data do not support the first conclusion, update the claim. This makes CER consistent with evidence-based reasoning rather than turning the claim box into a guess that must later be defended at all costs.

Evidence should bear directly on the claim. In an investigation, that may mean measurements, repeated observations, comparison groups, or a pattern across trials. In a source-based science task, it may come from a graph, model, text, or data table. Preserve units and conditions when they change the meaning of the result. A number without context is not automatically useful evidence.

Do not list every observation because it was collected. Ask which results discriminate among possible claims. NGSS materials repeatedly emphasize valid and reliable evidence and, at higher grades, multiple sources or lines of evidence when appropriate. Sufficiency depends on the task: a tightly scoped classroom question may sometimes be answered with one strong observation, but repeated observations are stronger when variability matters, and broader explanations may require several independent supports.

Reasoning is usually the hardest part because it cannot be copied directly from the data table. It identifies the scientific idea that makes the evidence meaningful. If an investigation shows ice melting faster on one surface, the reasoning needs the relevant thermal-energy relationship; repeating the melting times is still evidence, not reasoning. NSTA's CER guidance similarly distinguishes data from the justification that links data to a claim.

A useful prompt is: 'What science idea explains why this result supports my conclusion?' Another is: 'If a reader accepted the evidence but did not yet accept the claim, what relationship would I need to explain?' Those questions move students away from empty phrases such as 'This proves my claim' and toward an actual explanatory bridge.

Suppose a class tests how much water equal-sized pieces of two unlabeled paper-towel samples absorb, using the same water amount, contact time, draining method, and measurement procedure for both samples. Across three matched trials, Sample B absorbs more water each time. Claim: under the tested conditions, Sample B absorbed more water than Sample A. Evidence: the recorded amount for B is higher in all three matched trials, and the average for B is also higher. Those are observations from the investigation rather than opinions about which brand seems better.

Reasoning: using equal-sized samples while holding the water amount, contact time, draining method, and measurement procedure consistent makes the absorption results more comparable, and the repeated pattern across matched trials supports the conclusion that B performed better on this measured property under those conditions. Notice the limits. The CER does not justify a broader claim that B is 'the best paper towel' overall, because the investigation did not test cost, strength, different liquids, or every competing product. Good reasoning also keeps the conclusion proportional to what was tested.

The printable provides room for two pairs because many explanations benefit from more than one support. Pair one might describe the main quantitative pattern; pair two might identify a repeated observation, comparison, or second data source. Each reasoning box should explain the significance of that particular evidence instead of copying one generic sentence twice.

If the second piece adds nothing, do not force it. A requirement such as 'always use two pieces of evidence' can lead students to duplicate weak information. Conversely, a complex claim may need more than the worksheet provides. The organizer is a planning surface, not a rule about how much evidence science permits.

Real data are not always perfectly tidy. If one trial differs from the others, note it instead of silently discarding it. Check for measurement error, procedure differences, variability, or another explanation that the task allows you to investigate. The presence of an exception does not automatically destroy a claim, but the reasoning should not pretend contradictory evidence does not exist.

A stronger revision may narrow the claim: 'Sample B absorbed more water in two of three trials' is more accurate than a sweeping conclusion when the pattern is inconsistent. At advanced levels, students can discuss reliability, uncertainty, and competing explanations. The core habit stays the same: the claim and reasoning should respond to the evidence actually available.

Mistake one is writing a claim that simply repeats the question. Make a definite answer. Mistake two is putting an explanation in the evidence box. Ask whether the sentence reports what was observed or measured; if not, it may belong in reasoning. Mistake three is using every datum. Select information that directly bears on the claim. Mistake four is treating correlation as automatic causation when the investigation does not justify it.

Mistake five is repeating evidence in the reasoning section. Add the scientific principle or mechanism that explains the connection. Mistake six is keeping a claim that the results do not support. Revise it. Mistake seven is writing a conclusion broader than the study. Match the wording to the variables, samples, conditions, and evidence that were actually examined.

After planning, combine claim, evidence, and reasoning into connected prose. A short response may use one paragraph; a longer explanation may revisit the reasoning after several pieces of evidence. The reader should still be able to identify the three functions, but the final writing does not need to announce 'Claim:' and 'Evidence:' unless the teacher or assessment specifically requests those labels.

For younger learners, oral CER or color coding can make the distinctions visible before extended writing. For older students, add source evaluation, uncertainty, alternative explanations, and more demanding reasoning. The NGSS progression increases expectations for evidence and scientific reasoning across grade bands, so the scaffold should become more sophisticated as students gain knowledge rather than remain a fixed fill-in-the-blank routine.