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Claim-Evidence-Reasoning (CER)

by Model Teaching | January 29, 2019.


Have you ever had students respond, “I don’t know. It just did,” when asked to analyze and interpret their classroom lab results? We all want our students to “think like a scientist,” but often they fall short in connecting the dots between the lab results and the science concepts. Claim-Evidence-Reasoning or CER is a writing strategy that can develop a student’s analytical thinking and argumentative writing skills to turn that “I don’t know” into “aha, so that’s why we got those results in the lab.”


An Introduction to Claim-Evidence-Reasoning (CER)

What exactly is CER, and how does it work?

CER all starts with a question asked by the teacher. This question is based on a phenomena or lab experience. The student’s explanation or answer, as you may have guessed, will consist of three parts: a claim, the evidence, and the student’s reasoning.


  • A claim is a statement that answers the question. It will usually only be one sentence in length. The claim does not include any explanation, reasoning, or evidence so it should not include any transition words such as “because.”


  • The evidence is the data used to support the claim. It can be either quantitative or qualitive depending on the question and/or lab. The evidence could even be a data table the student creates. Students should only use data within their evidence that directly supports the claim.


  • The reasoning is the explanation of “why and how” the evidence supports the claim. It should include an explanation of the underlying science concept that produced the evidence or data.

Basic Tips to Implement CER Into the Classroom


When I introduce how to write a CER response in my classroom, I start with a non-science example. For students to be successful in writing a CER response, they must be able to make connections between their claim and evidence. If you start with something students are familiar with, they are more likely to fully understand what to write in each section. A non-science example I have used in the past is a Doritos commercial with the proposed question, “what happened to the cat?”

This commercial is fun for the students to watch, and students can easily justify their claim within their reasoning using evidence seen within the commercial. When students first write their claim-evidence-reasoning response, it is useful to provide a template for students to organize their thoughts. You can use the CER Graphic Organizer resource with your students to help them organize their thoughts during the early phases of CER writing.

Another useful technique when introducing CER to your students is collaboration. I first show the video to the class and students work in pairs to write a claim that answers the question, “what happened to the cat?”

  • Student Claim Example:  The dog killed the cat.
  • Student Evidence Example:  There is a cat missing poster. The dog is seen burying pet tags. The dog hands the man a bag of Doritos that says “You didn’t see nuthin.”

Last, I define the reasoning section, and students write their reasoning for “why” and “how” the evidence supports the claim. We then have a class discussion over the commercial and their written CER while crafting a whole group CER response to answer the question, “what happened to the cat?”


There was a missing poster posted of the cat which means the cat was missing. The cat was missing because the dog killed the cat and is covering up the murder. The dog is seen digging in dirt and covering up pet tags to hide the body of the cat. When someone is murdered, the body is usually hidden to hide the murder. If there are witnesses to the crime, they are often bribed to keep quiet about the crime. The man saw the dog burying the cat so he bribed the man with Doritos to keep him quiet about witnessing seeing the dog disposing of the cat’s body. This approach to introduce CER into your classroom provides the framework students will need to start writing CER responses in the lab setting.

CER Refinement

Argumentative reasoning is a skill that takes practice. This means that students will not write a perfect CER response their first attempt. They will need guidance and support from you, the teacher, as they write CER answers over labs conducted in class. It is useful for the teacher to model a sample CER response with the students in the beginning. However, students should first attempt to write their own CER response from the lab prior to the modeling. As you discuss with the class your sample CER response make sure you are emphasizing the concepts for a successful claim, evidence, and reasoning answer. Use the provided CER checklist to assist you with this discussion.

Students should use the CER Graphic Organizer resource as they continue to develop their writing skills and analyze their lab results. However, with continued use of CER their writing should become more refined and polished. Instead of the teacher modeling a sample response, students can now peer review answers and provide feedback to each other. At this point in your class, you have taught your students what it is truly like to think and write like a scientist!

This blog is intended to provide an overview for using the Claim-Evidence-Reasoning framework within your class. Use the provided resources for more information, implementation, and specific ideas for CER into your classroom.

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CER Checklist

A checklist for each section within a CER response is included here. It includes a detailed list of what should be included within the claim, evidence, and reasoning lessons for your students. The teacher can use this checklist when modeling CER responses in class. The checklist makes sure the student responses have all necessary components to write CER response.

CER Student Graphic Organizer

This is a graphic organizer for students to use to help organize their thoughts when writing CER responses. It will help students see the connection between the claim, evidence, and reasoning.


Use the CER checklist resource to evaluate your student’s growth in writing CER responses during lab activities. After CER has been modeled at least 3 times within your classroom, a student’s CER response should be written with at least 70% of the CER checklist items met.


  • NSTA – How Do You Know That?  Helping Students Write About Claims and Evidence – https://learningcenter.nsta.org/products/symposia_seminars/NSTA/files/HowDoYouKnowThat–HelpingStudentsWriteAboutClaimsandEvidence_12-12-2012.pdf
  • McNeill, KL, and DM Martin. “Claims, Evidence, and Reasoning.” Science and Children, vol. 48, no. 8, pp. 52–56.

A Collection of Resources for CER:




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