Teacher Reference
Claim, Evidence, Reasoning (CER)
Building evidence based thinking across every subject, with science and engineering examples.
Virtual Science Teachers
virtualscienceteachers.org
The three parts
What counts as strong depends on the subject and the question.C
Claim
Answers the question or states a conclusion.
What is your answer?
E
Evidence
Relevant data or observations that support the claim.
How do you know?
R
Reasoning
Uses science ideas to link the evidence to the claim.
Why does that evidence support it?
Easy ways to introduce it
Start with low pressure examples, before any formal task. Paths below are on virtualscienceteachers.org.
Commercials and videos
My Dad Is a Space Alien, She Shed, Doritos
Search these titles onlineFunny correlation graphs
Ice cream and shark attacks, shoe size and reading level
/correlation-vs-causation-graphsSix ways CER shows up in science and engineering
Common prompt types, not a rigid list.Classification
Use evidence and criteria to decide which category best fits.
Example
Based on the evidence, is this change physical or chemical?
Sample answer
CThis is a chemical change.
EThe steel wool warmed up, turned reddish brown, and gained 0.2 g after two days in damp air. Drying it off did not bring it back to its original state.
RA chemical change makes a new substance. The new color, the released heat, and the added mass together show the iron combined with oxygen to form rust, rather than just changing shape or state.
Comparison
Compare results gathered under the same conditions or criteria.
Example
Under the same conditions, which material reduced heat transfer the most?
Sample answer
CWool reduced heat transfer the most.
EStarting at 80°C, water in the wool wrapped cup was still 62°C after 20 minutes, compared with 55°C for foam and 48°C for cotton. Every cup held the same amount of water in the same room.
RThe best insulator is the one that lets the least energy escape. Wool traps more still air in its fibers, and trapped air is a poor conductor, so heat moved out of that cup more slowly.
Pattern or relationship
Use data to describe how quantities, conditions, or results are related.
Example
What relationship is shown between altitude and temperature?
Sample answer
CAs altitude increases, temperature decreases.
EThe graph falls steadily from 15°C at sea level, to 2°C at 2000 m, to 11°C below zero at 4000 m. That is a drop of about 6.5°C for every 1000 m gained.
RA steady downward slope shows an inverse relationship. Air thins with height and most of its warmth comes from the ground below it, so there is less to hold heat the higher you go.
Effect of a variable
Use a controlled test or strong evidence to examine how one factor affects another.
Example
Under the tested conditions, how does nitrate concentration affect algae growth?
Sample answer
CRaising nitrate concentration increased algae growth, but only up to a point.
EAfter 10 days, the 0, 5, and 10 mg/L tanks reached 12, 34, and 52 units of algae. The 20 mg/L tank reached 55, barely more than the 10 mg/L tank. Light, temperature, and starting algae were the same in all four.
RNitrate is a nutrient algae use to build new cells, so more of it supports more growth. The leveling off suggests that once nitrate was plentiful, something else such as light became the limiting factor.
Prediction
Use evidence, patterns, models, or prior cases to support what is likely next.
Example
Based on the data, what will likely happen if the food supply decreases?
Sample answer
CThe rabbit population will most likely fall.
EIn both earlier years when plant growth dropped, rabbit numbers fell the next season, from 240 to 150 and from 210 to 130.
RA population can only grow as large as its food supply supports. With less food, more rabbits go hungry and fewer survive to reproduce, so the same pattern should repeat.
Evaluate a solution
Use criteria, constraints, and test results to justify a design choice.
Example
Which bridge design best meets the criteria and constraints?
Sample answer
CThe truss design best meets the criteria and constraints.
EIt held 4.2 kg before failing, compared with 2.8 kg for the beam and 3.5 kg for the arch. It used 38 straws, under the 40 straw limit, while the arch used 46.
RThe design has to carry the most mass and stay within the material limit. The truss met both. The arch was strong but broke the constraint, so it does not qualify no matter how well it performed.
Evidence may include
observations
measurements
investigations
graphs and data
credible sources
calculations
models
design tests
Reasoning may draw on
accepted science concepts
definitions and criteria
cause and effect
models and mechanisms
math relationships
prior investigations
Correlation check
Two things changing together does not prove cause and effect. Ask: could another variable explain the pattern?
Evaluate the evidence and reasoning
Four questions to ask of any student response.1
Relevant
Does it directly support the claim and answer the question asked?
2
Sufficient and strong
Is there enough of it? Could another explanation fit just as well?
3
Trustworthy
Did it come from a fair method, accurate data, or a credible source?
4
Well reasoned
Does it link evidence to claim using science, without overclaiming?