CER Writing: Claim, Evidence, Reasoning

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Scientists do not just observe and collect data. They also explain what they learned. One way to write a scientific explanation is using CER: Claim, Evidence, and Reasoning.

What Is CER?

C = Claim: A sentence that answers a question. It tells what you think or found out.
E = Evidence: Facts, data, or observations that support your claim. This is proof!
R = Reasoning: Explains WHY your evidence supports your claim. It connects your evidence to your claim.

Think of CER Like This:

Claim: "I believe..." or "The answer is..."
Evidence: "I know this because..." or "The data shows..."
Reasoning: "This proves my claim because..." or "This makes sense because..."

Why Is CER Important?

CER helps you:

Explain your thinking clearly
Use evidence to support your ideas
Think like a real scientist
Write stronger answers on tests

Sentence Starters for CER

Claim starters:

"I think that..."
"The [animal/plant] shows..."
"Based on my observations..."

Evidence starters:

"I observed that..."
"The data shows..."
"For example..."

Reasoning starters:

"This supports my claim because..."
"This is important because..."
"This shows that..."

Examples

Example 1: Butterfly Life Cycle CER

Question: Does a butterfly look the same its whole life?

Claim: A butterfly does NOT look the same its whole life. It changes a lot as it grows.

Evidence: I observed that the butterfly starts as a tiny egg, then becomes a caterpillar with legs and stripes, then becomes a chrysalis that does not move, and finally becomes a butterfly with colorful wings.

Reasoning: This supports my claim because the butterfly looked completely different at each stage. An egg looks nothing like a caterpillar, and a caterpillar looks nothing like a butterfly with wings.

Example 2: Plant Growth CER

Question: Did the bean plant grow over 4 weeks?

Claim: Yes, the bean plant grew over 4 weeks.

Evidence: My data table shows the plant was 2 cm tall in Week 1 and 14 cm tall in Week 4. It grew 12 cm in total.

Reasoning: This proves my claim because the measurements show the plant got bigger each week. The number 14 is larger than 2, which means the plant grew.

Example 3: Comparing Life Cycles CER

Question: Are a frog's life cycle and a butterfly's life cycle similar?

Claim: A frog's life cycle and a butterfly's life cycle are similar because both animals change a lot as they grow.

Evidence: A frog starts as an egg, becomes a tadpole with a tail, grows legs, and becomes a frog. A butterfly starts as an egg, becomes a caterpillar, becomes a chrysalis, and becomes a butterfly.

Reasoning: Both animals go through big changes and look very different at each stage. A tadpole looks nothing like a frog, just like a caterpillar looks nothing like a butterfly. This is called metamorphosis.

Practice

Answer these questions about CER writing.

1. What does the "C" in CER stand for?

A) Caterpillar B) Claim C) Cycle D) Count

2. What does the "E" in CER stand for?

A) Egg B) End C) Evidence D) Example

3. What does the "R" in CER stand for?

A) Running B) Reasoning C) Reading D) Right

4. Which part of CER answers the question?

A) Claim B) Evidence C) Reasoning D) All three

5. Which part of CER gives facts or data to support your answer?

A) Claim B) Evidence C) Reasoning D) None of them

6. Which part of CER explains WHY your evidence supports your claim?

A) Claim B) Evidence C) Reasoning D) The title

7. Read this sentence: "The plant grew 5 cm in one week." Is this a Claim, Evidence, or Reasoning?

A) Claim B) Evidence C) Reasoning D) None of these

8. Read this sentence: "I think the caterpillar will become a butterfly." Is this a Claim, Evidence, or Reasoning?

A) Claim B) Evidence C) Reasoning D) None of these

9. Read this sentence: "This shows the plant needs water to grow because it only got taller when I watered it." Is this a Claim, Evidence, or Reasoning?

A) Claim B) Evidence C) Reasoning D) None of these

10. What is a good sentence starter for a CLAIM?

A) "The data shows..." B) "I think that..." C) "This is important because..." D) "For example..."

11. What is a good sentence starter for EVIDENCE?

A) "I observed that..." B) "I believe..." C) "This proves..." D) "The reason is..."

12. Why do scientists use CER?

A) To draw pictures B) To explain their thinking with proof C) To count things D) To run experiments faster

Check Your Understanding

Think about these questions to make sure you understand CER writing.

Can you explain what CER stands for?
What is the difference between evidence and reasoning?
Why is it important to support your claim with evidence?
Can you write a CER about something you observed in the life cycles unit?

Try It Yourself!

Write a short CER to answer this question: Do all living things go through changes as they grow?

Use what you learned about butterflies, plants, and frogs to write your Claim, Evidence, and Reasoning.

Next Steps

Practice writing CER responses for other science topics
Use sentence starters to help you get started
Complete the Unit Checkpoint to show what you learned