Claim Evidence Reasoning (CER): Examples, Rubric, Starters

Claim, Evidence, Reasoning (CER) is a three-part structure for writing a scientific explanation or argument: the claim answers the question, the evidence is the data or text that backs it up, and the reasoning explains why that evidence proves the claim.

CER comes from science education. Katherine McNeill and Joseph Krajcik developed it to help middle school students write explanations of lab results, and ELA and history teachers picked it up because "answer the question, then prove it" isn't only a science skill.

Most students can make a claim. Plenty can find evidence. Reasoning is where it falls apart, so that's where this page spends most of its time.

The three parts of CER

We'll use one lab for all three parts. Students plant bean seeds in six cups. Three go on a sunny windowsill and three go in a dark closet, with the same soil and the same water. After ten days, the class measures them.

Here's the sample data:

Yes, the closet plants are taller. Seedlings in the dark stretch upward looking for light. Many students expect the opposite and write it anyway, which makes this a good lab for teaching them to trust the data over the prediction.

Claim

The claim is a one-sentence answer to the question. In a lab it's the conclusion. In an essay it does the job of a thesis.

The question here is "How does light affect the growth of bean seedlings?" Three claims a teacher will see:

• "Plants need sunlight." True, and it doesn't answer the question about this lab.
• "The plants in the sun grew taller." The ruler says otherwise.
• "The seedlings in the dark grew taller, but only the seedlings in light grew healthy green leaves." That one works.

A quick test: does it answer the question in one sentence, and could the data have proven it wrong? If the claim would be true no matter what the cups looked like, it's too vague.

Evidence

Evidence is what students observed, measured, read or found in a source. In science it's data. In ELA it's quotations. In history it's documents.

The fix teachers make most often here is "be specific." "The data shows it" is not evidence. Neither is "The closet plants looked bad." Strong evidence has numbers with units, or exact words with a page or paragraph number:

"After ten days, the closet seedlings averaged 15 cm and the windowsill seedlings averaged 9 cm. The closet seedlings were pale yellow with thin stems, and their leaves hadn't opened. The windowsill seedlings were green with open leaves."

Watch for the opposite problem too. Some students copy the entire data table into the evidence box. Evidence means picking the numbers that matter for the claim, and that choice is part of the thinking.

Reasoning

Reasoning explains why the evidence supports the claim, usually by bringing in a rule or concept the class has learned. It's the part that shows whether a student actually understands the science.

What students write when they don't have it yet:

• "The plant grew because it's alive."
• "This proves my claim."
• "Because of photosynthesis."

The last one is close. It names the right idea and then stops. What it needs is the connection:

"A bean seed stores food in its cotyledons, so a seedling can grow for a while without light. In the dark, it uses that food to stretch upward, which is why the closet plants were taller. But plants need light to make chlorophyll, the green pigment they use for photosynthesis. Without chlorophyll the closet seedlings couldn't make new food, so their leaves stayed yellow and small. When the stored food runs out, they'll stop growing."

A check that works on student drafts: does the reasoning contain an idea that isn't already in the claim or the evidence? If it only repeats them, it isn't reasoning yet. On the board, try the frame "Because ___, which means ___." It forces the second half.

More CER examples

Science: Alka-Seltzer and water temperature

Question: Does water temperature affect how fast an Alka-Seltzer tablet reacts?

• Claim: The tablet reacts faster in warmer water.
• Evidence: In ice water, the tablet took 95 seconds to stop fizzing. In room-temperature water it took 50 seconds, and in hot tap water it took 25 seconds. We used the same amount of water and one whole tablet each time.
• Reasoning: The fizzing is a chemical reaction between the citric acid and baking soda in the tablet, which makes carbon dioxide gas. In warmer water the particles move faster, so they collide more often and with more energy, and the reaction happens faster. Because the amount of water and tablet were the same in every trial, temperature is what changed the time.

Expect a few students to write "dissolves." It's worth a minute to point out that bubbles mean a new gas is forming.

ELA: "The Tell-Tale Heart"

Question: Is the narrator of Edgar Allan Poe's "The Tell-Tale Heart" reliable?

• Claim: The narrator is unreliable.
• Evidence: In the first paragraph, the narrator asks how anyone could call them mad, then claims to have "heard all things in the heaven and in the earth." At the end, with the old man dead and hidden under the floorboards, the narrator hears a heartbeat growing louder until they confess.
• Reasoning: A reliable narrator gives an account readers can trust. This one insists on being sane while describing sounds no person could hear, including the heartbeat of a dead man. The gap between what the narrator says about themselves and what they describe tells readers not to take the story at face value.

Social studies: the Erie Canal

Question: How did the Erie Canal affect New York City?

• Claim: The Erie Canal helped New York City pull ahead of rival ports like Philadelphia and Baltimore.
• Evidence: Document A, a map, shows the canal linking Lake Erie to the Hudson River, which runs to New York City. Document B, a merchant's letter, says farm goods from the Great Lakes now reach New York faster and more cheaply by canal boat than they did by wagon.
• Reasoning: Trade follows the cheapest route. The canal gave farms in the new western states a water route that ended in New York instead of another East Coast city. As more goods passed through the port, the city gained shipping and business its rivals didn't.

In a DBQ, CER pushes students to say what each document shows instead of summarizing it.

Math, briefly

Is 3/8 bigger than 1/3? Claim: yes. Evidence: 3/8 = 9/24 and 1/3 = 8/24. Reasoning: once the denominators match, the pieces are the same size, so the fraction with more pieces is bigger.

CER sentence starters

Starters help the student who knows the answer and stares at the blank box anyway. Put them on an anchor chart or at the top of the page, and take them away once students stop needing them.

Claim

• I claim that...
• Based on the data, ...
• In this text, the author shows that...

Evidence

• According to the data, ...
• On page ___, the text says "..."
• Document ___ shows that...
• Another piece of evidence is...

Reasoning

• This evidence supports my claim because...
• Because ___, which means ___.
• The science idea that explains this is...
• If my claim were wrong, we would expect to see ___ instead.

Save the last one for older students. It's hard.

If you'd rather not build the page yourself, Eduaide's CER worksheet generator makes a printable worksheet from your topic and grade level, with a question, a data set and a labeled box for each part.

A simple CER rubric

Score each part on its own so students can see which one needs work. A missing part scores 0.

If reasoning is the skill you're teaching this unit, count that row double. Otherwise a student can earn 6 out of 9 without explaining anything.

Teaching CER for the first time

1. Start with no content at all (10 minutes). Show a photo of an empty cookie jar and a kid with crumbs on their shirt. Ask who ate the cookies. Students give a claim, point to the clues, and say why the clues matter. Nobody's stuck on vocabulary.
2. Name the parts. Make an anchor chart with Claim, Evidence and Reasoning, a one-line definition of each, and the cookie example.
3. Model one out loud. Write a CER on the board using your current unit and talk through your choices, especially the reasoning. "I have my evidence. Now, why does a taller plant in the dark make sense?"
4. Sort the strips (15 minutes). Cut a finished CER into sentence strips, plus one sentence that only restates the claim. Pairs sort them into claim, evidence and reasoning. The fake reasoning strip starts the best arguments.
5. Write one as a class from a question and a small data set, and let students argue over each sentence.
6. Have students write their own with starters and a three-column organizer. You can sketch one on paper or use one of Eduaide's graphic organizers.
7. Score and revise. Have students score an anonymous sample with the rubric before revising their own. The reasoning row is usually where the revisions happen.

Mistakes to watch for

Reasoning that repeats the claim. "This proves plants need light" is the claim again with "this proves" in front. Keep asking "Why does that evidence prove it?" until a concept shows up.

"My evidence is the data." Ask which numbers.

Explanation leaking into the evidence. Students write "The closet plants were taller because they were looking for light" in the evidence box. Evidence is what was seen or stated. The "because" belongs in reasoning.

Claims bigger than the evidence. One lab with six cups can't prove "light is important for all plants." Have students cut the claim down to what the data can show.

Using CER for everything. It's built for questions that need an argument. A vocabulary quiz doesn't need it, and students tire of the format fast if it's on every assignment.

Differentiating CER

Younger students or students who need more support

• Use plain labels: Claim = "my answer," Evidence = "how I know," Reasoning = "the rule that connects them."
• Do it out loud first, to a partner, before writing a word.
• Give a word bank that includes the concept they'll need for the reasoning.
• Let them pick evidence from a short list instead of hunting through a whole passage. One good piece is enough at first.

English language learners

• Use frames that carry the grammar, like "The data shows that ___ because ___."
• Pre-teach claim, evidence and support, plus signal words like because, therefore and this shows.
• Let students plan or talk it through in their home language before writing in English.
• Put a small icon next to each part on the anchor chart and worksheet.

Students ready for more

• Require evidence from two different sources.
• Ask them to answer a counterclaim, which turns CER into CERR.
• Have them judge the evidence itself. Are three plants per group enough? Would they trust a merchant's letter more than a map?

CER FAQ

What does CER stand for?

CER stands for Claim, Evidence, Reasoning. The claim answers the question, the evidence supports the claim, and the reasoning explains why the evidence supports it.

What is the difference between evidence and reasoning?

Evidence is what you observed or read. Reasoning is the rule or concept that explains why that evidence proves your claim. "The closet plants were yellow" is evidence. "Plants need light to make chlorophyll" is reasoning.

Is CER only for science?

No. It started in science, but it works anywhere students argue for an answer, from a character analysis to a cause in history. The evidence changes. The structure doesn't.

What is the difference between CER and CERR?

CERR, sometimes written CER-R, adds a fourth part, usually a rebuttal: students name an opposing claim and explain why their evidence outweighs it. Some teachers use the extra R for reflection instead, so check which version your school or curriculum uses. Most classes add the rebuttal once plain CER feels routine.

How long should a CER response be?

In upper elementary and early middle school, three to five sentences is plenty: one claim, one or two pieces of evidence, a sentence or two of reasoning. High school students working from several sources may write a full paragraph or more. Length matters less than whether the reasoning explains the connection.