A bank of finished Claim, Evidence, Reasoning (CER) paragraph examples across biology, chemistry, physics, ELA, history, and math, complete with sentence-by-sentence breakdowns.
A Claim, Evidence, Reasoning (CER) example is a structured paragraph where a writer makes an assertion, supports it with measured data or direct observations, and explains the scientific principle that connects the two. At Chalkbox, we design classroom writing materials and generator tools for teachers who need reliable models that students can study during a lesson. A standard CER paragraph runs three to five sentences: one claim sentence, one to two evidence sentences citing specific data, and one to two reasoning sentences that state the governing rule. When students see this structure applied to concrete lab findings, they learn to separate what they observed from the broader scientific rule that explains why it happened.
A complete CER paragraph contains three distinct parts that move from a specific conclusion to supporting data and then to an established scientific rule.
Here is an annotated physical science model showing all three elements working in sequence:
[Claim] Increasing the temperature of water speeds up the rate at which granulated sugar dissolves.
[Evidence] In the class trial, five grams of granulated sugar dissolved in 100 milliliters of water at 60 degrees Celsius in 18 seconds, whereas the same mass of sugar took 54 seconds to dissolve in 100 milliliters of water at 20 degrees Celsius.
[Reasoning] Higher temperatures give water molecules greater kinetic energy, which makes them collide with sugar particles more frequently and break the intermolecular bonds faster.
This example succeeds because the claim answers an investigative question directly without using filler words. The evidence provides quantified measurements from two distinct conditions rather than a vague observation. The reasoning names the governing mechanism, kinetic energy and molecular collisions, to justify why the higher temperature produced faster dissolution.
Biology CER examples demonstrate how living organisms respond to environmental variables or internal physiological demands.
Claim: Bean plants produce more vegetative growth when grown under direct sunlight than when grown in darkness.
Evidence: Over a fourteen-day period, bean seedlings placed on a sunny windowsill grew an average of 14 centimeters and produced six dark green leaves per stem, while seedlings placed in a lightproof closet grew an average of 4 centimeters and developed pale yellow leaves before wilting.
Reasoning: Plants require light energy to perform photosynthesis, the biochemical process that converts water and carbon dioxide into glucose for cell division and structural tissue growth.
Why this works: The evidence pairs clear numerical growth measurements with physical color observations across two controlled conditions, and the reasoning identifies the exact biochemical process responsible for that difference.
Claim: Aerobic exercise causes a rapid increase in human heart rate above resting levels.
Evidence: Student pulse measurements averaged 71 beats per minute while seated at rest, but rose to an average of 136 beats per minute immediately following three minutes of jumping jacks.
Reasoning: Contracting muscle cells consume oxygen and adenosine triphosphate (ATP) rapidly during physical activity, requiring the heart to pump blood faster to supply oxygenated blood and remove carbon dioxide waste.
Why this works: The claim answers the investigation question directly, the data pairs pre-exercise and post-exercise heart rates, and the reasoning explains the cellular oxygen demand that drives circulation changes.
Physical science and chemistry CER examples explain observable changes in matter using atomic properties and physical laws.
Claim: Adding sodium chloride to liquid water lowers its freezing point below zero degrees Celsius.
Evidence: A beaker containing 200 milliliters of pure water froze solid at zero degrees Celsius, but an identical volume of water containing twenty grams of dissolved table salt remained liquid until the freezer reached minus six degrees Celsius.
Reasoning: Dissolved salt ions interfere with the ability of water molecules to bind into a rigid hexagonal ice crystal lattice, which forces the system to reach a colder temperature before crystallization can occur.
Why this works: The evidence contrasts the freezing point of pure water against the salt solution with specific temperature values, and the reasoning cites the structural lattice formation of ice molecules.
Claim: A solid aluminum block sinks in water because its physical density is greater than the density of liquid water.
Evidence: The aluminum sample had a measured mass of 54 grams and displaced 20 milliliters of water, yielding a calculated density of 2.7 grams per cubic centimeter, compared to the known density of water at 1.0 gram per cubic centimeter.
Reasoning: An object sinks in a fluid whenever the gravitational pull on its mass exceeds the upward buoyant force produced by the volume of fluid it displaces.
Why this works: The student calculated the physical density from collected mass and volume values, and the reasoning applies Archimedes' principle of buoyant forces to explain why the block sank.
Physics and Earth science CER examples explain mechanical interactions and natural geological processes through physical principles.
Claim: Increasing the starting height of a ramp increases the speed of a toy cart at the base of the track.
Evidence: Releasing the cart from a ramp height of 10 centimeters produced an average speed of 1.2 meters per second at the track base, whereas releasing the cart from a height of 30 centimeters produced an average base speed of 2.4 meters per second.
Reasoning: Raising the cart to a higher elevation increases its gravitational potential energy, which converts into greater kinetic energy and higher velocity as the cart rolls down the track.
Why this works: The paragraph contrasts two starting release heights with their measured velocity values, and the reasoning uses energy conservation laws to connect potential energy to kinetic energy.
Claim: Surface vegetation reduces the volume of topsoil lost to rainfall runoff.
Evidence: When two liters of water were poured over a sloped tray of bare topsoil, 190 grams of sediment collected in the drainage beaker, while an identical soil tray covered with rooted grass turf lost only 24 grams of sediment under the same water flow.
Reasoning: Dense root networks anchor loose soil particles together, while plant leaves and stems absorb the physical impact of falling water, slowing down surface runoff and preventing it from carrying soil granules away.
Why this works: The evidence records exact runoff sediment weights, and the reasoning describes the mechanical stabilization provided by roots and plant stems.
An English Language Arts (ELA) CER example adapts the scientific framework by using textual details and character actions as evidence and literary concepts as reasoning.
Claim: In A Christmas Carol by Charles Dickens, Ebenezer Scrooge undergoes a genuine moral transformation from an isolated miser into a generous community member.
Evidence: In the opening stave, Scrooge rejects charity collectors by arguing that destitute citizens should enter workhouses or die to decrease the surplus population, but in the final stave, he secretly sends a prize turkey to the Cratchit household and pledges an immediate raise to Bob Cratchit's salary.
Reasoning: These contrasting actions show that Scrooge stops treating social obligations as monetary losses and instead accepts personal responsibility for vulnerable people around him, fulfilling the author's theme of spiritual redemption.
Why this works: The claim asserts character change across the narrative arc, the evidence sets up contrasting textual events from the beginning and end of the book, and the reasoning connects those actions to broader thematic meaning.
A history CER example explains the causes or consequences of historical events by linking primary source records to economic or political principles.
Claim: The opening of the Erie Canal in 1825 stimulated rapid commercial expansion between the Atlantic seaboard and Midwestern agricultural territories.
Evidence: Before the canal opened, moving one ton of freight from Buffalo to New York City cost roughly one hundred dollars and took twenty days over rough roads, but canal transit reduced shipping fees to under ten dollars per ton and cut transit time to eight days.
Reasoning: Drastic reductions in freight transport costs enabled frontier farmers to sell surplus grain profitably in eastern urban centers, creating strong financial incentives for merchants and settlers to build new commercial towns along the canal waterway.
Why this works: The claim states a clear economic outcome, the evidence quantifies freight rates and travel durations from historical trade records, and the reasoning explains the economic supply-and-demand incentives that resulted.
A mathematics CER example requires students to justify an answer by presenting calculated figures as evidence and mathematical definitions or theorems as reasoning.
Claim: Purchasing the twenty-four pack of juice boxes for fifteen dollars is a better financial value than purchasing individual juice boxes at eighty cents each.
Evidence: Dividing fifteen dollars by twenty-four boxes yields a unit price of 62.5 cents per box, whereas purchasing twenty-four individual boxes at eighty cents each costs nineteen dollars and twenty cents in total.
Reasoning: Comparing unit costs proves that the bulk package saves 17.5 cents per box, meaning the buyer spends less money per fluid ounce for the identical product.
Why this works: The claim answers a comparison question, the evidence shows the step-by-step arithmetic, and the reasoning explains why unit cost calculations determine financial value.
Comparing weak and strong CER paragraphs reveals that unsuccessful attempts usually stumble by stating personal opinions instead of data or by simply restating the claim as reasoning.
Here is an example of a weak student response on plant biology:
Weak: Plants grow better in the light because they like the sun. We noticed that our plant in the window grew taller and looked healthier than the plant in the dark closet. This proves that light makes plants grow because the sun is good for them.
Here is the revised, strong version of the same assignment:
Strong: Sunlight increases bean plant vertical growth and leaf production. Over fourteen days, the seedling placed in the window grew nine centimeters and produced six green leaves, whereas the seedling in the dark closet grew two centimeters and developed yellowing leaves. Sunlight provides the photon energy required for chloroplasts to carry out photosynthesis, which creates the glucose molecules plants use for cellular expansion.
Three concrete fixes transform the weak paragraph into a high-scoring response:
Sentence starters help students organize their thoughts into the three distinct stages of argumentative writing without getting bogged down by paragraph transitions.
Claim Starters:
Evidence Starters:
Reasoning Starters:
The CER framework is not the right tool for exploratory lab notebooks, broad narrative writing, or open-ended literary interpretation where no single claim resolves the text. Multi-source research papers, contested historical ethics, and raw open-inquiry lab notes all resist a single claim. Forcing them into one CER paragraph strips out the nuance. For those extended assignments, building an essay outline or writing open dialectical arguments gives students the room they need to examine multiple viewpoints.
Our recommendation to use CER models flips if an assignment shifts from demonstrating mastery of a known scientific principle to evaluating competing hypotheses with incomplete or contradictory data. When advanced students analyze ambiguous datasets where several interpretations hold equal weight, a single rigid claim misrepresents the uncertainty. Assign a structured critique or a comparative analysis paper instead.
Teachers introduce CER writing most effectively by providing finished mentor paragraphs before asking students to draft their own responses. For lesson plans and scaffolding strategies, see our guide on how to teach CER writing. To provide physical graphic organizers for students to map out their claims and data during lab time, print the CER template. When you are ready to evaluate student writing consistently across sections, use our free rubric generator to build an aligned scoring guide.
Select one claim evidence reasoning example from the subject sections above and project it on the board. Ask students to highlight the claim in blue, the evidence in yellow, and the reasoning in green before they write their own.
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To properly write a CER, begin with a single claim sentence that directly answers the guiding question without extra opinion. Follow the claim with one or two evidence sentences that cite specific numbers, measurements, or direct observations from your investigation. Finish with one or two reasoning sentences that identify the scientific principle connecting your evidence to your claim.
A good CER presents an accurate claim, relies on specific measured data rather than vague observations, and explains the underlying mechanism using established concepts. It avoids circular logic where the writer simply restates the claim at the end. The entire paragraph remains concise, typically running between three and five complete sentences.
Useful claim starters include 'The data indicates that' or 'Increasing [variable X] causes [variable Y] to.' For evidence, use 'According to our measurements' or 'During the trial, the control group recorded.' For reasoning, use 'This occurs because the principle of [concept] dictates that' or 'These results connect to [mechanism] because.'
One common biology CER example examines photosynthesis, claiming that bean seedlings grow taller in direct sunlight than in darkness, citing growth measurements in centimeters, and using the photosynthetic production of glucose as reasoning. Another example investigates human circulation, claiming that physical exercise increases pulse rate, citing before-and-after heart rate numbers, and explaining how muscle tissue demands faster oxygen delivery during exertion.
This guide provides educational writing models and instructional advice for teachers and students. Verify specific rubric requirements with your school or district curriculum guidelines before assigning grades.