CER Writing
Learn how to write like a scientist using Claim, Evidence, and Reasoning.
Learn
Scientists do not just do experiments. They also have to explain what they learned. CER writing is a special way scientists share their ideas. CER stands for:
- C = Claim: What you think or what you found out
- E = Evidence: The data or facts that support your claim
- R = Reasoning: Why the evidence supports your claim
What is a Claim?
A claim is your answer to a question. It is what you believe is true based on your investigation.
- A claim is a statement, not a question
- It answers the question you were investigating
- It should be clear and specific
Example Question: Which ball bounces higher, a tennis ball or a basketball?
Example Claim: The tennis ball bounces higher than the basketball.
What is Evidence?
Evidence is the data or facts from your investigation that support your claim.
- Evidence comes from what you observed or measured
- Use numbers when you can
- Evidence must come from your investigation, not what you already thought
Example Evidence: When dropped from 3 feet, the tennis ball bounced 2 feet high. The basketball only bounced 1 foot high.
What is Reasoning?
Reasoning explains WHY your evidence supports your claim. It connects your evidence to your claim using science ideas.
- Use words like "because," "this shows," or "this means"
- Explain the science behind what happened
- Tell why your evidence proves your claim is correct
Example Reasoning: This shows the tennis ball bounces higher because 2 feet is more than 1 foot. The tennis ball is smaller and lighter, which helps it bounce back up more.
Putting It All Together
A complete CER looks like this:
Question: Which ball bounces higher?
Claim: The tennis ball bounces higher than the basketball.
Evidence: When dropped from 3 feet, the tennis ball bounced 2 feet high, and the basketball only bounced 1 foot high.
Reasoning: This shows the tennis ball bounces higher because 2 feet is greater than 1 foot. The tennis ball may bounce higher because it is smaller and lighter than the basketball.
Examples
Example 1: Ice Melting
Question: Does ice melt faster in warm water or cold water?
Claim: Ice melts faster in warm water than in cold water.
Evidence: The ice cube in warm water (80F) melted in 2 minutes. The ice cube in cold water (40F) melted in 8 minutes.
Reasoning: This shows warm water melts ice faster because 2 minutes is much less time than 8 minutes. Warm water has more heat energy, which makes the ice melt quicker.
Example 2: Paper Airplanes
Question: Which paper airplane design flies the farthest?
Claim: The dart airplane flies farther than the glider airplane.
Evidence: The dart flew 15 feet. The glider flew 9 feet. I tested each airplane 3 times and measured with a measuring tape.
Reasoning: My evidence shows the dart flies farther because 15 feet is more than 9 feet. The dart's pointed shape might help it cut through the air better.
Example 3: Plant Growth
Question: Do plants grow better near a window or away from a window?
Claim: Plants grow better near a window.
Evidence: After 2 weeks, the plant near the window grew 4 inches tall. The plant away from the window only grew 1 inch tall.
Reasoning: This proves plants grow better near windows because 4 inches is much more than 1 inch. Plants need sunlight to grow, and there is more sunlight near the window.
Example 4: Magnet Strength
Question: Which magnet is stronger?
Claim: The big magnet is stronger than the small magnet.
Evidence: The big magnet picked up 12 paper clips. The small magnet picked up 5 paper clips.
Reasoning: My data shows the big magnet is stronger because it picked up more paper clips (12 is greater than 5). Bigger magnets often have more magnetic force.
Practice
Answer these questions about CER writing.
1. What does CER stand for?
Show Answer
B) Claim, Evidence, Reasoning
2. What is a claim?
Show Answer
C) Your answer or what you found out - A claim is a statement that answers your question.
3. Which is an example of evidence?
Show Answer
B) The red car finished in 5 seconds, the blue car finished in 8 seconds - This is data from an observation or measurement.
4. What does reasoning do?
Show Answer
C) Explains why the evidence supports the claim - Reasoning connects your evidence to your claim.
5. Read this claim: "Sugar dissolves faster in hot water." Which evidence supports this claim?
Show Answer
B) Sugar dissolved in hot water in 10 seconds, in cold water in 45 seconds - This data shows hot water dissolved sugar faster.
6. Which word helps connect evidence to a claim in reasoning?
Show Answer
B) Because - Words like "because," "this shows," and "this means" help explain reasoning.
7. A student writes: "The plant in soil A grew taller." This is an example of:
Show Answer
C) A claim - This is a statement about what was found out.
8. A student writes: "Plant A grew 6 inches. Plant B grew 3 inches." This is an example of:
Show Answer
B) Evidence - These are measurements (data) from the investigation.
9. Where does evidence come from?
Show Answer
B) Your investigation or experiment - Evidence must come from what you observed or measured.
10. A student writes: "This shows the bigger ball is heavier because 500 grams is more than 200 grams." This is an example of:
Show Answer
C) Reasoning - This explains WHY the evidence supports the claim using "this shows" and "because."
11. What comes first when writing a CER?
Show Answer
C) Claim - First state your claim, then give evidence, then explain your reasoning.
12. Which is the BEST claim for answering "Which paper towel absorbs the most water?"
Show Answer
C) Brand X absorbs the most water - This directly answers the question with a clear statement.
Check Your Understanding
Challenge 1: Read this investigation and write a complete CER.
Investigation: Maya tested which type of soil helps bean plants grow tallest. She planted one bean in sandy soil and one bean in potting soil. After 3 weeks, the bean in sandy soil was 2 inches tall. The bean in potting soil was 7 inches tall.
Show Sample Answer
Claim: Bean plants grow taller in potting soil than in sandy soil.
Evidence: After 3 weeks, the bean in potting soil grew 7 inches tall, but the bean in sandy soil only grew 2 inches tall.
Reasoning: This shows potting soil helps bean plants grow better because 7 inches is much more than 2 inches. Potting soil probably has more nutrients that plants need to grow tall and healthy.
Challenge 2: A student wrote this CER. Find what is missing or needs to be fixed.
"Claim: The wooden ramp makes cars go faster. Evidence: I like wooden ramps. Reasoning: Wood is better than plastic."
Show Sample Answer
Problem with Evidence: "I like wooden ramps" is an opinion, not data. The evidence should include measurements, like "The car on the wooden ramp traveled 5 feet in 2 seconds. The car on the plastic ramp traveled 3 feet in 2 seconds."
Problem with Reasoning: "Wood is better than plastic" does not explain WHY the evidence supports the claim. Better reasoning: "This shows the wooden ramp makes cars go faster because the car traveled farther in the same amount of time."
Next Steps
- Practice identifying claims, evidence, and reasoning in science writing
- Try writing your own CER after your next investigation
- Move on to the next lesson: Unit Checkpoint