Student writing in notebook

The Secrets of CER: a Step-by-Step Guide for Science Teachers

February 18, 2023 No Comments

If you are here, you likely are interested in using the CER framework in your science class. This is an excellent framework for integrating writing into your science lessons. And, it helps students create clear, written arguments. But, there are challenges with using the CER format. Read the post below to get all of your questions about the CER framework answered.

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What is a CER?

A CER (Claim-Evidence-Reasoning) is a tool used in science classes to help students think critically and support their ideas. It is a three-step process that requires students to make a statement, provide evidence to support their statement, and explain the logic behind their statement. A claim is an opinion or idea about a scientific concept or phenomenon. The evidence is the data or research that supports the statement, and the logic is what connects the evidence to the statement. By using the CER tool, students are able to explain their scientific understanding and develop their critical thinking skills.

To learn more about the parts of an argument, click here.

How is a CER used in science?

A CER is used to create a well-structured argument that answers a question about a scientific phenomenon. Students use this framework to write an argument when there is more than one possible claim or answer to a question. Therefore, because there is more than one answer, an argument is formulated to support one potential claim over the others.

Limitations of CER

I like to consider the CER a scaffold for the practice of argumentation. In order to make good arguments, it’s important that students understand the parts of an argument. And, this structure works well when arguments are written.

However, we also want our students to engage in verbal discourse in the classroom. In most cases, students won’t argue using the CER format during verbal discussions. Therefore, this is a helpful scaffold. But, ideally, this wouldn’t be the only way that argumentations would take place in the science classroom.

Creating CER Scenarios for Your Science Students: Step-by-Step

Step 1: Pick Your Topic

The first step is determining what topic you want students to investigate in your classroom. Ideally, this is related to your anchoring phenomenon in some way. However, if you haven’t developed extensive storylines yet, that’s okay. Start with a topic you want students to learn about. I like to write down the associated NGSS performance expectation.

Step 2: Come up with two (or more) potential claims.

Remember, you want your students to write an argument. Therefore, there must be more than one potential explanation. Otherwise, there isn’t an argument.

So, you need to come up with potential claims related to the argument. How do you do that?

Address student misconceptions with alternate claims.

I like to address student misconceptions about a topic. And luckily, there is a bank of students’ misconceptions for you to utilize. This is the CAST Item Specifications.

This resource is intended to help item writers for California’s state science test. However, it also includes student misconceptions about each performance expectation. Therefore, this is a great way to come up with alternate claims.

I STRONGLY suggest sticking to two potential claims, at least at first. Having at least two claims makes it possible for an argument to occur. However, more potential claims will lead to confusion. This is especially true when you introduce this skill. Later, once students have some practice, it’s possible to add additional claims.

Still, the best way to come up with alternate claims is from experience. As you get to know your student population, you’ll begin to recognize misconceptions that they have about different topics.

Example of Alternate Claims

When I was teaching high school chemistry, I noticed that very few of my students could explain why condensation collected on the outside of a cold beverage.

Condensation on the top of a soda can
Many students believe that soda leaks out of the can, causing condensation on the outside. This is an example of an alternate claim you could include when creating a CER.

In fact, many students believed that condensation is caused by a beverage leaking out of the container. This misconception makes a great alternative argument to how condensation actually forms on the outside of a can.

Step 3: Decide on an investigative phenomenon (or more than one).

Next, you’ll need investigative-level phenomena for students to investigate. These investigative pieces allow students to decide which claim is correct.

Ideally, these investigative phenomena you present lead to multiple pieces of evidence. These pieces of evidence support one or more of the claims. By giving students multiple pieces of evidence, you present students with the opportunity to sort the evidence. Then, they use the evidence to determine which claim is correct.

Example Investigative Phenomena

Let’s go back to the condensation example. How do students know that the beverage is not actually leaking out of the can? Here are a few things you can do:

  1. Have students find the mass of the can before and after condensation forms. (The change is likely minimal, so be sure to use a precise scale.)
  2. Ask students to observe the color of the liquid on the outside of several different cold beverages. Make sure the beverages are different colors.
  3. Give students access to the PhET States of Matter Simulation. Ask them how thermal energy affects particle motion.

There are countless other activities that help students understand this concept.

But, we can also present students with information that supports the alternate claim.

Rusty soda can
Present students with some information that supports the alternate claim. However, the majority of the evidence should point to the correct claim.

For example, my friend found some old soda cans in her garage. The cans were fully intact. However, the cans were much lighter than expected. This led us to believe that the cans were somewhat permeable. This fact supports the claim that a beverage could leak out of the container.

Still, the majority of the evidence presented shows that condensation comes from moisture in the air. It’s okay to present students with evidence that supports the alternate claim. But, make sure that the majority of the evidence supports the correct claim.

Step 4: Draft Your Storyline

Many teachers are intimidated by the term storyline. However, a storyline is just the order in which you present information to students. The storyline is well thought out so student understanding becomes clear over time.

To learn more about storylines, click here.

Think about the order that you will present the information. I like to move from simple to more complex. For example, I’d start the lesson sequence with things that are more directly observable. Asking students to observe the liquid coming from various beverages is VERY simple. (In fact, this might be too simple for your students!)

Then, I’d use the PhET simulation toward the end of the lesson sequence. Simulations are a great piece to add as an explanation tool if you follow the 5E model.


Ideally, storylines are complex lesson sequences that cover multiple standards. However, it’s not always possible to build these robust storylines. This is especially true when you are just getting started with the NGSS.

Nicole VanTassel from iExploreScience explains the benefits of building simple storylines in this episode of the Teaching Science in 3D podcast.

These simple storylines are great for CER activities.

Step 5: Pick your CER scaffolds to teach students to use CERs to write arguments.

You’ve successfully set up your CER scenario. But, if you want to be truly successful, it’s important to plan scaffolds for your students. These scaffolds will look different depending on how much experience your students have with CER. If they have never used the CER framework, I highly recommend focusing ONLY on the claim and evidence for the first go-round.

Interactive Notebook.  The left side is a title "identifying the claim, evidence, and reasoning." There are paragraphs where there area parts highlighted in different colors.
Here is an example of one of the scaffolds I use. I like to have students highlight the parts of their CER. Click here to learn more.

Highlighting Parts of an Argument

One trick that works very well is having students highlight the parts of an argument. Highlight the claim, evidence, and reasoning in different colors. This strategy helps you quickly identify students who are struggling with this concept. Click here to view my resources, which include this highlighting activity.

The CER (Claim-Evidence-Reasoning) framework helps students create well-structured arguments and develop their critical thinking skills. While the framework is incredibly useful for teaching argumentation, there are some limitations. To learn more about the practice of engaging in an argument, check out this blog post.

Erin Sadler

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