Claim-evidence-reasoning, often shortened to CER, is a staple of science classrooms because it breaks an argument into three parts that students can learn to recognize. Chemistry commentaries about everyday life, such as those in Joe Schwarcz's "Radar, Hula Hoops, and Playful Pigs," are excellent raw material for CER writing. Each commentary contains claims about how something works, evidence in the form of observations or experiments, and reasoning that links the two. Students can practice by reconstructing that argument in their own words.

The challenge for teachers is that students often blur the three parts together. A claim gets repeated as evidence, or the reasoning is replaced by a restatement of the claim in slightly different words. When you grade, you need a way to separate these quickly, so that feedback can say exactly which part is weak rather than offering a general comment about "needs more support."

One effective habit is to annotate each essay with three colors, one for each component, before assigning a score. A paper with plenty of claim color and almost no reasoning color tells you immediately where the problem lies. This takes a few extra minutes at first, but after a dozen papers you can usually identify the pattern at a glance.

Common weaknesses in student CER writing

The most frequent weakness is evidence that is not actually evidence. Students write that "everyone knows" a household product behaves a certain way, or they cite the author's conclusion as if it were data. Teaching them to ask whether a reader could check the statement independently is a powerful correction, and you can build that question directly into your feedback.

• Claims that are too broad to test, such as saying a substance is "good" or "bad" without specifying how.
• Evidence that restates the claim instead of offering an observation, measurement, or documented example.
• Reasoning that jumps from evidence to conclusion without naming the scientific principle connecting them.
• Overreliance on a single example when the claim needs support from more than one case.
• Missing counterevidence, where a stronger essay would acknowledge a limit or exception.

Writing feedback that points to the exact gap

Compare two comments on the same paper. The first says "strengthen your reasoning." The second says "you state that heating changes the substance; add one sentence explaining what happens to the molecules that makes this a chemical change." The second comment gives the student a task they can finish in five minutes, and it models what good reasoning looks like in chemistry.

Keep a bank of reusable comments for common gaps, adjusted to each student's wording. This speeds up grading without making feedback generic, and it ensures that two students with the same weakness receive the same quality of guidance regardless of whether their paper was graded first or last.

Scoring CER consistently across a large class

A three-row rubric, one row per component, makes scoring straightforward. Give each row a four-point scale and describe in one sentence what each point looks like. The total score then reflects the balance of the argument rather than the overall impression, which tends to favor fluent writers over careful thinkers.

When classes are large, inconsistency creeps in from fatigue and from drift in your own standards. Regrading the first few papers at the end of a session is a simple check, and AI grading tools can provide a second, steady reference point that applies the same rubric to every essay in the same way.

Using revision to turn feedback into learning

Feedback only matters if students do something with it. Build a short revision step into the assignment, requiring students to rewrite the weakest component and submit a note saying what they changed. This also tells you whether the student understood your comment, which is often more informative than the original essay.

Over several commentary assignments, you should see students improve at separating evidence from reasoning. Tracking this growth in a simple chart gives you something concrete to share at parent conferences or department meetings, and it shows that the writing work is building real scientific thinking skills.