CER is a three-part frame for any answer that has to prove itself. State the answer in one sentence, back it with data, then explain why the data settles it. The last move is the one that gets graded. Science teachers grade lab conclusions with it, English teachers grade paragraphs with it, and the structure is identical both times.
MIT's BLOSSOMS resource sheet compresses it to a single line: claim is what you know, evidence is how you know it, reasoning is your thought process. Most students nail the first two. The third is where the grade is decided.
The Sentence Budget
Six sentences, roughly. A CER response has a standard shape:
| Part | Length | Job |
|---|---|---|
| Claim | 1 sentence | Answer the question directly. No "I think," no restating the prompt. |
| Evidence | 1-2 sentences | The data, quote, or observation. Specific, with numbers or page references. |
| Reasoning | 2-3 sentences | The rule or principle that makes the evidence prove the claim. |
Notice the proportions. Reasoning gets the most room because it does the most work. If your reasoning is one sentence and your evidence is three, the paragraph is upside down.
What Counts as Reasoning
Reasoning names the rule that connects evidence to claim. It is not a restatement of the evidence in different words, which is the mistake behind most "add more reasoning" comments in the margins.
The test: your reasoning should contain a general principle that would still be true even without your specific evidence. In science, that's the underlying concept. In an essay, it's the definition or standard your argument leans on. Evidence is always the specific. Reasoning is the general rule behind it, and the claim is where the two meet.
One more diagnosis, courtesy of the science teachers who grade these daily: weak reasoning usually starts as weak evidence. If the data doesn't clearly bear on the question, no amount of explaining connects it. When the reasoning won't come, check the evidence before rewriting the explanation.
- Need the claim-to-evidence links laid out visually? The Graphic Organizer Generator builds a cause-and-effect chart, pre-filled or blank, so you can see where the connection breaks.
- Want to see how paragraphs carry each move? The Paragraph Structure Explainer breaks a paragraph into its parts and explains what each one does.
Three Worked Examples
Science. Claim: Heating a magnet weakens it. Evidence: The magnet held 20 paperclips before heating and 8 after reaching 80°C. Reasoning: Heat adds thermal energy, which knocks the metal's magnetic domains out of alignment. Fewer aligned domains means a weaker field, so the paperclip drop is exactly what the physics predicts.
English. Claim: The protagonist is resilient. Evidence: After losing her home and job, she starts volunteering at the community center rebuild. Reasoning: Resilience means recovering from setbacks quickly. Choosing to rebuild something for others, immediately after losing her own foundations, is that definition in action.
History. Claim: Economic pressure drove the American Revolution. Evidence: The Stamp Act of 1765 taxed all colonial paper goods and triggered organized boycotts. Reasoning: When a policy hits every household's finances at once, resistance organizes fast. The boycotts show colonists acting as an economic bloc before they acted as a political one.
One skeleton, three subjects. That's the point of the frame: learn it once and the reasoning move transfers. NGSS lists "engaging in argument from evidence" as a core science practice for exactly that reason.
- Writing up a lab? The Lab Report Template structures every section, so the CER lands in the discussion where the grader looks for it.
- Answering a history prompt? The DBQ Essay Writer drafts a defensible thesis backed by document evidence and sourcing analysis.
- Taking a position in English class? The Argumentative Essay Writer runs claim, evidence, and reasoning across a full essay.
How to Start a CER
Start with the claim, and start the claim with the answer itself. If the question is "does salt lower the freezing point of water," the claim is "salt lowers the freezing point of water." Restating the question, or opening with "In this experiment we tested," burns the sentence where the answer belongs.
A claim that can't be argued with can't be graded well either. If nobody could raise a counterclaim against it, it isn't a claim yet. "Temperature affects magnets" is too soft to prove. If yours reads like that, a thesis statement generator sharpens it into one arguable sentence, and for lab reports a hypothesis generator frames the claim as a testable prediction before the data ever comes in.
Where Students Lose the Points
Restating instead of reasoning. "The magnet held fewer paperclips, which shows heating weakened it" repeats the evidence with a verb change. The grader is looking for the domain physics, the definition, the principle.
Evidence without a number. "The magnet held fewer paperclips" is weaker than "20 before, 8 after." If you measured it, say the measurement.
The buried claim. Three sentences of setup before the answer appears. In a CER, sentence one is the answer. Everything else exists to defend it.
- Want a rubric check before you submit? The Essay Grader scores a response against a rubric and names the specific fixes.
From CER to Full Paragraphs
A body paragraph is a CER wearing essay clothes: the topic sentence is the claim, the textual evidence is the data, and the analysis is the reasoning. A body paragraph writer builds that structure with all three parts present, which is a fast way to see the frame at essay scale. Draft the response in the Dock Editor (free for 7 days) and the claim, data, and sources stay in one document while you tighten the reasoning.
Next lab report or essay paragraph, write the reasoning sentence before the evidence sentence. Knowing the principle you're proving tells you which data earns a place, and the "add more reasoning" comment never shows up.