Claim Evidence Reasoning

What is Claim, Evidence, Reasoning (CER)?

CER is a powerful framework used in science education to help students develop critical thinking and analytical skills. Standing for Claim, Evidence, and Reasoning, it provides a structured approach to formulating scientific arguments and explanations. By using CER, students can effectively analyze data from scientific investigations and construct well-supported conclusions.

Here’s how it works:

Claim: This is a statement or answer to a scientific question. It’s what you think or what you’ve found out. For example, “Plants grow faster in sunlight.”
Evidence: These are the facts, data, or observations that support your claim. It’s important that evidence is gathered through experiments, observations, or research. For the above claim, evidence could be, “In a two-week experiment, plants in sunlight grew three inches, while those in the dark grew only one inch.”
Reasoning: This links your evidence to your claim. It’s the scientific principle or understanding that explains why your evidence supports your claim. For our example, the reasoning might be, “Photosynthesis, which is necessary for plant growth, requires sunlight. The plants in the sunlight had more opportunity for photosynthesis, hence they grew more.”

How to Write Strong CER Responses

Claim (Answer the Question Clearly)

What to Include in a Claim:

✔ Restate important parts of the question to make your claim clear.
✔ Provide a concise answer based on the investigation or data.
✔ Avoid explanations—just state what you know.

Sentence Starters for Claims:

The data shows that…
The results support the idea that…
Based on the evidence, I conclude that…
The experiment demonstrated that…

Evidence (Support Your Claim with Data or Observations)

What to Include in Evidence:

✔ Source of evidence (experiment, graph, data table, or observations).
✔ Quantitative data (numbers) or qualitative data (descriptions).
✔ Be specific—avoid vague phrases like “there was a change.”

Sentence Starters for Evidence:

According to the data, [describe key result]…
In the experiment, we observed that…
The graph/table shows that…
The data supports the claim because…

Reasoning (Explain Why the Evidence Supports the Claim)

What to Include in Reasoning:

✔ Scientific principles or background knowledge that explain the evidence.
✔ Connect the data to the scientific concept behind it.
✔ Clearly explain why the evidence proves the claim.

Sentence Starters for Reasoning:

This happens because…
This is explained by the scientific principle that…
Since [scientific concept], the results make sense because…
This connects to [scientific idea] because…

Final Tip: Check Your CER Response!

✅ Does the claim answer the question clearly?
✅ Does the evidence directly support the claim with specific data?
✅ Does the reasoning explain why the evidence is scientifically valid?

Why use CER?

Develops Critical Thinking: CER helps students think more deeply about how they draw conclusions from data.
Improves Communication: Students learn how to construct and articulate logical, evidence-based arguments.
Encourages Scientific Inquiry: CER mirrors the process scientists use, fostering a better understanding of scientific methods.

CER Examples

Question:

How does surface area affect water evaporation?

Claim:

Water evaporates faster when it has a larger surface area.

Evidence:

After 24 hours, 40 mL of water evaporated from the wide dish, while only 15 mL evaporated from the narrow beaker, showing that a larger surface area leads to faster evaporation.

Reasoning:

Evaporation happens when water molecules gain energy and turn into gas. A larger surface area allows more molecules to escape at once, speeding up evaporation, while a smaller surface area limits exposure, slowing it down.

Question:

How does light direction affect plant growth?

Claim:

Plants grow towards light sources.

Evidence:

In an experiment, plants near a window leaned towards the light over time.

Reasoning:

Plants respond to light through phototropism, where cells on the shaded side elongate, causing the plant to bend toward the light. This helps maximize light absorption for photosynthesis, allowing the plant to grow efficiently.

Question:

How does heating a magnet affect its strength?

Claim:

Heating a magnet decreases its magnetic strength.

Evidence:

Magnets were tested by picking up paperclips before and after heating. Before heating, they held 20 paperclips; after being heated to 80°C, they held only 8, showing a loss in strength.

Reasoning:

Heat makes atoms vibrate more, disrupting their alignment and weakening the magnetic field, reducing the magnet's strength.

Question:

How does salt affect water's freezing point?

Claim:

Salt lowers the freezing point of water.

Evidence:

Two containers of water were placed in a freezer—one with pure water and one with saltwater. The pure water froze at 0°C, while the saltwater remained liquid until -5°C.

Reasoning:

Salt lowers the freezing point of water by interfering with the formation of ice crystals. Dissolved salt ions hinder water molecules from bonding as solid ice, thus requiring colder temperatures to freeze, a process known as freezing point depression.

Question:

How does an object's weight affect how fast it falls in a vacuum?

Claim:

In a vacuum, an object's weight does not affect how fast it falls.

Evidence:

In a vacuum, a heavy and light object were dropped simultaneously. Both hit the ground at the same time, showing weight does not affect falling speed.

Reasoning:

Without air resistance, the only force acting on the objects is gravity, which accelerates all objects at the same rate regardless of their mass.