Claim-Evidence-Reasoning, often shortened to CER, is a practical structure for turning scientific knowledge into a defensible answer. The core aim of Science mastery is not to train students to fill three labelled boxes mechanically. It is to help them make a clear claim, select evidence that actually matters and explain the scientific relationship connecting the evidence to the claim.
For students and parents searching for Claim Evidence Reasoning, CER in Science, CER examples, scientific argument, evidence-based answers or how to write a Science explanation, the most useful principle is this: evidence does not speak for itself. A good answer must show why the selected evidence supports the conclusion.
CER is therefore a bridge between data and explanation.
The 60-Second CER Structure
Claim: What do you conclude?
Evidence: What observation, measurement, graph, table or result supports that conclusion?
Reasoning: Why does that evidence support the claim according to scientific ideas?
A strong CER answer should feel like one connected argument rather than three unrelated sentences.
Wait, What? Evidence Is Not the Same as Reasoning?
Correct.
Evidence is what the investigation or source shows.
Reasoning is the scientific explanation that connects that evidence to the claim.
Example:
Claim: Material A is the better thermal insulator.
Evidence: After 20 minutes, water in Material A cooled by 4°C while water in Material B cooled by 9°C.
Reasoning: A smaller temperature decrease indicates less energy transfer from the water to the surroundings under the same conditions.
The evidence gives the result. The reasoning gives the meaning.
What Makes a Good Claim?
A good scientific claim should be:
- clear;
- specific;
- answer the actual question;
- proportional to the evidence;
- free from unnecessary certainty.
Instead of:
“Material A is best.”
Use:
Under the tested conditions, Material A reduced heat loss more effectively than Material B.
The claim now matches the evidence range.
What Counts as Evidence?
Evidence may include:
- measurements;
- repeated readings;
- graph trends;
- table values;
- observations;
- experimental comparisons;
- results from reliable research.
Good evidence is relevant to the claim.
A large amount of irrelevant data does not make an argument stronger.
Reasoning Is the Missing Middle
Students often write:
“The plant grew taller because it got more light.”
This may be directionally correct but incomplete.
A stronger response includes the mechanism:
More light can increase the rate of photosynthesis within the relevant range, increasing the production of substances needed for growth, provided other important factors are not limiting.
The reasoning explains why the evidence supports the claim.
CER and Open-Ended Science Questions
CER is especially useful when a question asks students to:
- explain;
- justify;
- conclude;
- evaluate a claim;
- use data to support an answer.
See Science Open-Ended Questions.
CER and Scientific Conclusions
A conclusion often contains a claim supported by evidence.
CER adds the reasoning layer that shows why the evidence justifies the conclusion.
Use Scientific Conclusion for the conclusion skill.
CER and Evidence-Based Reasoning
CER is a structured version of broader evidence-based reasoning.
It helps students ask:
- What am I claiming?
- Which evidence matters most?
- Which concept connects the evidence to the claim?
A Worked Example: Reaction Rate
Question:
Which condition produced the fastest reaction?
Claim: The highest tested temperature produced the fastest reaction.
Evidence: It had the shortest measured reaction time.
Reasoning: A shorter time to the same endpoint indicates a faster rate under otherwise comparable conditions.
A Worked Example: Plant Growth
Claim: Plants receiving the medium light level grew more than plants receiving the lowest light level.
Evidence: Their mean increase in height was greater over the same 14-day period.
Reasoning: The growth measure was collected over aligned conditions, so the difference supports a relationship between the tested light level and measured growth.
If control variables were weak, the claim should be more cautious.
CER and Competing Explanations
Strong reasoning considers whether another explanation fits the evidence.
Ask:
- Could another variable have caused the difference?
- Is the evidence large enough to matter?
- Does an anomaly weaken the pattern?
- Does the scientific model support the proposed mechanism?
This connects to Science Critical Thinking.
Primary Science CER
Primary students can use:
I think ___ because the results show ___, and this means ___.
The scaffold can be removed gradually as reasoning becomes more fluent.
Secondary Science CER
Secondary students should increasingly include:
- quantitative evidence;
- scientific models;
- uncertainty;
- limitations;
- alternative explanations;
- claim strength.
How to Practise CER
Take one graph or table and write:
- one claim;
- two pieces of evidence;
- one scientific reason connecting them;
- one limitation that affects confidence.
Then check whether the reasoning really explains why the evidence supports the claim.
Common CER Mistakes
- claim does not answer the question;
- evidence is vague;
- evidence is copied without interpretation;
- reasoning simply repeats the evidence;
- reasoning gives theory unrelated to the data;
- claim is stronger than the evidence allows.
Frequently Asked Questions
What is Claim-Evidence-Reasoning?
It is a structure for scientific argument where a claim is supported by relevant evidence and connected through scientific reasoning.
What is the difference between evidence and reasoning?
Evidence is the observation or data. Reasoning explains why that evidence supports the claim.
Does every Science answer need CER?
No. Simple state or calculate questions may not. CER is especially useful for explanation, justification and evidence-based questions.
How can I improve CER answers?
Use specific evidence, explain the scientific mechanism and keep the claim proportional to the data.
Useful eduKateSG Routes
The Core Aim
Claim-Evidence-Reasoning teaches students to make scientific answers defensible.
State the claim. Select the evidence. Explain the link.
That is the core aim: make every important scientific answer show not only what the student thinks, but why the evidence deserves that conclusion.
Properly taught kids shine a bright light into the future.