CER Writing: Claim, Evidence, Reasoning
Learn
Scientists do not just say what they think - they explain their thinking! When scientists share their ideas, they use a special way of writing called CER. CER stands for Claim, Evidence, and Reasoning.
What Is CER?
C = Claim
Your claim is your answer to a question. It tells what you think or what you found out.
Example: "Ice is a solid."
E = Evidence
Your evidence is the proof. It comes from what you observed, measured, or read. Evidence is facts, not opinions.
Example: "When I touched the ice, it was hard and kept its shape. It did not pour like water."
R = Reasoning
Your reasoning explains WHY your evidence supports your claim. It connects your evidence to science ideas.
Example: "This shows ice is a solid because solids have their own shape and do not flow. Solids keep their shape unless something changes them."
Why Use CER?
- It helps you explain your thinking clearly
- Other people can understand how you got your answer
- It shows you used real evidence, not just guessed
- Scientists all around the world use CER to share their discoveries
CER Sentence Starters
Use these sentence starters to help you write CER:
| Part | Sentence Starters |
|---|---|
| Claim |
"I think that..." "My claim is..." "The answer is..." "[Object] is a [solid/liquid/gas] because..." |
| Evidence |
"I observed that..." "My data shows..." "In the experiment, I saw..." "The evidence is..." |
| Reasoning |
"This shows that... because..." "This evidence supports my claim because..." "This makes sense because..." "Scientists know that..." |
A Complete CER Example About States of Matter
Question: Is orange juice a solid, liquid, or gas?
Claim: Orange juice is a liquid.
Evidence: When I poured orange juice from a carton into a glass, it flowed and took the shape of the glass. When I poured it into a bowl, it took the shape of the bowl. It did not keep its own shape.
Reasoning: This shows orange juice is a liquid because liquids flow and take the shape of their container. Liquids do not have their own shape like solids do. The orange juice acted just like other liquids.
Examples
Example 1: Identifying the Parts of CER
Read this CER and find each part:
"A rock is a solid. When I put the rock on the table, it stayed the same shape. It did not flow or spread out. This shows it is a solid because solids keep their shape no matter where you put them."
Answer:
- Claim: "A rock is a solid."
- Evidence: "When I put the rock on the table, it stayed the same shape. It did not flow or spread out."
- Reasoning: "This shows it is a solid because solids keep their shape no matter where you put them."
Example 2: Finding Missing Parts
This CER is missing a part. What is missing?
"The balloon has gas inside. When I squeezed the balloon, I could feel air pushing back. The balloon felt full even though I could not see anything inside."
Answer: The reasoning is missing! A complete CER would add: "This shows there is gas inside because gases spread out to fill their container and push against the sides. Even though we cannot see air, it takes up space."
Example 3: Good Evidence vs. Weak Evidence
Question: Is milk a liquid?
Weak evidence: "Milk is a liquid because I like to drink it."
Good evidence: "When I poured milk from the jug, it flowed into my cup and took the shape of the cup."
Why is the second one better? Good evidence describes what you observed. Liking something is an opinion, not evidence!
Practice
Answer these questions about CER writing.
1. What does the "C" in CER stand for?
- A) Container
- B) Claim
- C) Change
- D) Color
2. What does the "E" in CER stand for?
- A) Example
- B) Experiment
- C) Evidence
- D) Energy
3. What does the "R" in CER stand for?
- A) Reading
- B) Reasoning
- C) Running
- D) Recording
4. Which part of CER answers the question?
- A) Evidence
- B) Reasoning
- C) Claim
- D) None of them
5. Which is an example of good evidence?
- A) "I think ice is cold."
- B) "Ice is my favorite."
- C) "When I touched the ice, my fingers got cold and wet."
- D) "Ice is pretty."
6. Read this sentence: "Water flows and takes the shape of its container." This is an example of:
- A) A claim
- B) Evidence
- C) An opinion
- D) A question
7. Read this sentence: "This shows water is a liquid because liquids take the shape of their container." This is an example of:
- A) A claim
- B) Evidence
- C) Reasoning
- D) A prediction
8. Why do scientists use CER?
- A) To confuse people
- B) To explain their thinking clearly
- C) To make writing longer
- D) To hide their answers
Read this CER and answer questions 9-10:
"Steam is a gas. When water boiled in the pot, I saw steam rising into the air. The steam spread out and disappeared. This shows steam is a gas because gases spread out and fill the space around them."
9. What is the claim in this CER?
- A) "Water boiled in the pot."
- B) "Steam is a gas."
- C) "Gases spread out."
- D) "The steam disappeared."
10. What evidence did the writer use?
- A) Steam is invisible
- B) Water is a liquid
- C) Steam rose into the air, spread out, and disappeared
- D) Pots are made of metal
Check Your Understanding
Try writing your own CER! Choose one of these questions and write a complete CER with a claim, evidence, and reasoning.
- Question: Is a pencil a solid, liquid, or gas?
- Question: What happens to water when you put it in the freezer?
- Question: Is the air around us a solid, liquid, or gas?
Checklist for your CER:
- Did you state your claim (answer) clearly?
- Did you include evidence from what you observed or know?
- Did you explain WHY your evidence supports your claim?
- Did you use science words like solid, liquid, gas, shape, flow, or spread?
Next Steps
- Practice writing CER responses about everyday objects
- When you see something interesting, ask yourself: "How would I explain this using CER?"
- Use the sentence starters to help you get started
- Continue to the Unit Checkpoint to review everything you learned about states of matter