Write Claims Supported by Evidence
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Learning Objectives
- 1Write a clear claim that answers a science question in one sentence
- 2Cite specific data as evidence to back up the claim
- 3Connect evidence to the claim with reasoning that uses a science rule
- 4Distinguish a strong, data-backed claim from a weak opinion claim
Mini Lesson
After you run a fair test and collect reliable data, the next job is to say what the data means. Scientists do not just shout an opinion. They write a claim, then they back it up with evidence, then they explain the science rule that links the two together. This three-part structure — Claim, Evidence, Reasoning — is how every real scientific argument is built. Learn it once and you can write a strong conclusion for any experiment.
The Three Parts of a Scientific Argument
- Claim — a one-sentence answer to the question your experiment was asking.
- Evidence — the actual data from your trials, with numbers and units.
- Reasoning — the science rule that explains why your evidence supports your claim.
What Makes a Claim Strong
- It directly answers the question. No drifting off topic.
- It is specific. It names what changed and what was measured.
- It is neutral. No "I think" or "I feel" — it states what the data shows.
- It is testable. Another scientist could check it by running the same experiment.
- It is short. One clean sentence is enough.
What Counts as Evidence
Evidence is the data you actually wrote down — measurements, counts, times, observations from your trials. Evidence is not your guess and not what other people said online. Strong evidence comes from your own trials, with units, and ideally from more than one trial so you can show the result was repeatable.
- Numbers from measurements: 18 cm, 22 g, 14 seconds.
- Counts: 7 sprouted seeds out of 10.
- Averages across multiple trials: average growth was 4.2 cm per week.
- Direct observations: the salt water cup had no crystals; the sugar water cup had visible crystals after 2 days.
How Reasoning Connects Them
Reasoning is the bridge. It takes the science rule you already know — like "plants need light to make food" or "warmer molecules move faster" — and uses it to explain why the evidence you collected supports the claim you made. Without reasoning, your claim looks like a coincidence. With reasoning, it becomes an explanation.
Question: Does sunlight affect how tall bean plants grow in 2 weeks?
Write a Claim, Evidence, and Reasoning paragraph from these results: light plant grew to 18 cm, dark plant grew to 7 cm, both started at 2 cm.
Notice how the claim is one sentence, the evidence cites the actual numbers from the trial, and the reasoning ties the data to a science rule (photosynthesis).
Strong Claim vs Weak Claim
- STRONG: Plants in sunlight grew an average of 11 cm more than plants kept in the dark over 2 weeks.
- WEAK: I think sunlight is the best thing for plants.
- STRONG: Sugar dissolved in 8 seconds in hot water and 26 seconds in cold water.
- WEAK: Hot water is way better for dissolving stuff.
- STRONG: 7 of 10 fertilizer-treated seeds sprouted; 3 of 10 untreated seeds sprouted.
- WEAK: Fertilizer is good. Everyone knows that.
Tip: when you write a claim, point at your data table while you say it out loud. If your claim does not match what your numbers show, rewrite the claim — never bend the data.
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