Claim-Evidence-Reasoning (CER) Generator
Type your claim, your evidence one data point per line, and the scientific principle that connects them. The generator writes a claim-evidence-reasoning paragraph in three wordings, labels each part, and checks your draft against what a CER answer needs. Honest templates, no AI. Free, no sign-up.
The question your claim answers. It also lets the checklist test that it does.
One sentence that answers the question. No “I think”.
Data or observations from your investigation — one per line, with units.
The scientific principle that explains why your evidence supports your claim.
Your CER paragraph
Add a claim, evidence, and reasoning to build the paragraph.
Writing about a text rather than an experiment? The PEEL Paragraph Planner suits literary and historical evidence better.
What each part needs
These checks read words and numbers, not meaning — a tick says a feature is present, not that the science is right.
Claim
- States the claim in one sentenceCheck yourself
- States it directly, without “I think” or “I believe”Check yourself
- Answers the question that was askedCheck yourself
- Says the data support the claim, not that they prove itCheck yourself
Evidence
- Gives specific data — measurements or observationsCheck yourself
- Includes a unit with each measurementCheck yourself
- Uses more than one piece of evidenceCheck yourself
- Every piece of evidence relates directly to the claimCheck yourself — Cut any data point that does not bear on the claim — extra numbers dilute the paragraph.
Reasoning
- Names the scientific principle, law, or concept that links evidence to claimCheck yourself — Name the rule itself, e.g. “light energy drives photosynthesis” or “particles move faster when heated.”
- Explains the science instead of repeating the dataCheck yourself
- Develops the reasoning in a full sentence or twoCheck yourself
How to Use the Claim-Evidence-Reasoning (CER) Generator
- 1. Add the question (optional). Paste the investigation question so the paragraph can open with it and the checklist can test that your claim answers it.
- 2. Write your claim. One sentence that answers the question — “the rate of photosynthesis increases as light intensity increases”.
- 3. List your evidence. One measurement or observation per line, with units. The generator links the lines with “In addition,” and “Finally,” or “First,” and “Next,” so they read as a sequence.
- 4. Explain the reasoning, then check the list. State the principle that connects your data to your claim, and fix anything marked Worth a look before you copy a version.
What Each Part of CER Does
| Part | What it is | What it needs |
|---|---|---|
| Claim | A one-sentence answer to the question | A direct, testable statement about the investigation — not “I think”. |
| Evidence | The data or observations that support the claim | Specific values with units, enough of them to show a pattern, all relevant to the claim. |
| Reasoning | The scientific principle that explains why the evidence supports the claim | A named concept or rule — energy transfer, inheritance, conservation of mass — applied to your data rather than a repeat of it. |
The framework comes from science-education research: Katherine McNeill and Joseph Krajcik set it out for middle-school classrooms in Supporting Grade 5–8 Students in Constructing Explanations in Science (2012). Some teachers add a fourth part, rebuttal, in which students explain why an alternative claim is weaker — a version often called CERR.
Worked Example
Try an example loads a classic pondweed experiment with illustrative results: the plant sits 10, 30, and 50 cm from a lamp, and the oxygen bubbles it releases are counted. Version 2 opens with the question and closes by tying the principle back to the data:
Version 2
How does light intensity affect the rate of photosynthesis in pondweed? The results show that the rate of photosynthesis increases as light intensity increases. For example, at 10 cm from the lamp, the pondweed released an average of 28 oxygen bubbles per minute over three trials. In addition, at 30 cm, the average fell to 11 bubbles per minute. Finally, at 50 cm, it fell to 4 bubbles per minute. These results make sense because light supplies the energy for the light-dependent reactions of photosynthesis, which split water and release oxygen, so a brighter light lets the plant produce oxygen faster until another factor, such as carbon dioxide, becomes limiting. Because the data follow the pattern this principle predicts, they support the claim.
Every automatic check passes for this input: the claim is one direct sentence that shares its key words with the question, the evidence has numbers and units across three data points, and the reasoning explains rather than repeats them. Two items stay with you — whether every data point bears on the claim, and whether the reasoning names a real principle. Here it does, and it even adds the limit (carbon dioxide) that explains why the rate cannot rise forever.
CER vs. PEEL
Both structures make a claim and back it up, but they belong to different subjects. CER answers a scientific question with data; PEEL — point, evidence, explanation, link — builds a body paragraph in an essay, where the evidence is usually a quotation or example and the explanation is interpretation. For a paragraph about a text or a historical event, use the PEEL Paragraph Planner.
| Feature | CER | PEEL |
|---|---|---|
| Used in | Science classes and lab reports | Essays in English, history, and the social sciences |
| Opens with | A claim that answers a question | A point that supports the thesis |
| Evidence is | Measurements and observations | Quotations, examples, and statistics from sources |
| Third part | Reasoning: a general scientific principle | Explanation: your interpretation of the evidence |
| Ends with | The reasoning (or a rebuttal, in CERR) | A link back to the thesis |
Common Mistakes
- Evidence that is really a conclusion. “The plant did better in bright light” is a summary; “28 bubbles per minute at 10 cm” is evidence.
- Reasoning that repeats the data. If your reasoning quotes the numbers again, it is still evidence. Reasoning explains why the pattern happens.
- A claim that hedges or overreaches. “I think light might matter” is too weak; “this proves light is the only factor” is too strong. Claim what your data support.
- Missing units. “The temperature rose by 12” could mean degrees Celsius, degrees Fahrenheit, or something else entirely.
Frequently Asked Questions
- What does CER stand for?
- CER stands for claim, evidence, reasoning. The claim answers a question, the evidence is the data that supports it, and the reasoning is the scientific principle that explains why the evidence supports the claim. It is widely used in middle- and high-school science to teach students to write scientific explanations.
- What is the difference between evidence and reasoning in CER?
- Evidence is what you observed or measured: numbers, observations, results. Reasoning is why that evidence supports the claim, stated as a scientific principle. If a sentence could be checked against your data table, it is evidence; if it explains the science behind the pattern, it is reasoning.
- How long should a CER paragraph be?
- Usually five to eight sentences: one for the claim, two to four for the evidence, and one or two for the reasoning. In student drafts the reasoning is often the shortest part, yet it should be the most developed, because it is where scientific understanding shows.
- Can a CER claim be wrong?
- Yes. A claim is only as strong as the evidence behind it, and an experiment can produce data that contradict your hypothesis. The honest claim is the one your data support, and the reasoning explains what happened — a well-argued unexpected result is better science than a forced expected one.
- What is CERR?
- CERR adds a fourth part, rebuttal, to claim, evidence, and reasoning. After making the case, you explain why an alternative claim is wrong or less supported by the data. Use it when your teacher asks for it or when there is an obvious competing explanation.
- Does the generator write my lab conclusion?
- No. It arranges the claim, data, and reasoning you type into standard sentence frames — honest templates, no AI. The checklist reads surface features such as numbers, units, and the word “prove”; it cannot judge whether your science is correct. The wording checks (hedges such as “I think”, the word “prove”, unit names, and key words shared with the question) work on English text only; on translated pages the checklist runs just the checks that do not depend on English wording.