Evidence, Reasoning and Conclusions
Your plants grew taller in bright light. That is a result. But how do you turn that result into a conclusion you can actually defend, and not claim more than your data shows?
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A student tests how the drop height of a ball affects its bounce. At 20 cm it bounces 12 cm, at 40 cm it bounces 25 cm, and at 60 cm it bounces 37 cm. They conclude: "Balls always bounce higher when dropped from higher."
Is that conclusion fully supported by the data? What part of it goes further than the evidence allows?
A strong scientific conclusion has three connected parts, often called CER. The claim is your answer to the investigation question, a short statement of what you found. The evidence is the specific data from your investigation that backs up the claim, the actual measurements, not a feeling. The reasoning is the sentence or two that explains why that evidence supports the claim, linking the two together.
Think of it like a courtroom. The claim is what you are trying to prove, the evidence is the exhibits you point to, and the reasoning is the lawyer explaining how the exhibits prove the case. Leave out the evidence and it is just an opinion. Leave out the reasoning and the reader has to guess how your numbers connect to your claim. All three together make a conclusion you can defend.
Claim: Warmer water dissolves sugar faster. Evidence: At 20°C the sugar took 90 s to dissolve, at 40°C it took 55 s, and at 60°C it took 30 s. Reasoning: The dissolving time fell each time the temperature rose, so the data shows a clear link between higher temperature and faster dissolving.
When the Bureau of Meteorology reports that a region is drying out, it does not just say "it feels drier". It states the claim, points to the evidence (rainfall totals falling over decades), and gives the reasoning (each decade's average sits below the last). Naming all three is what makes the statement trustworthy.
A claim on its own is not a conclusion, it is just an opinion until you attach the evidence and the reasoning. "Bright light is best" with no numbers behind it would not convince any scientist.
Know
- A conclusion is built from a claim, evidence and reasoning.
- Evidence is specific data, not a feeling or a guess.
Understand
- How data from an investigation becomes evidence for a claim.
- Why reasoning is needed to link the evidence to the claim.
Can Do
- Write a conclusion that uses claim, evidence and reasoning.
- Judge whether a conclusion is well supported or overreaches the data.
Wrong: A conclusion is just whatever you believe after the experiment.
Right: A conclusion is a claim backed by specific evidence and clear reasoning.
Wrong: "The plants grew well" counts as evidence.
Right: Evidence is the numbers, such as "4 cm, 7 cm and 11 cm".
Wrong: If a result is clear, you can drop the reasoning.
Right: Reasoning tells the reader exactly how the evidence proves the claim.
Wrong: One test of one plant type proves a rule for all plants.
Right: A conclusion should stay within what was actually tested.
A student writes three sentences in a conclusion. One of them is not supported by the data, click it.
- Adding more salt lowered the boiling time, from 300 s down to 265 s.
- The boiling time fell each time more salt was added.
- At 100 g of salt the water would not boil at all.
Let's build one from real data. The question was: "Does the amount of light affect the height of bean seedlings after two weeks?" Three trays were grown under low, medium and bright light, with everything else kept the same. The measured heights were 4 cm (low), 7 cm (medium) and 11 cm (bright). Now turn that into a conclusion using all three CER parts.
Claim: "In this investigation, bean seedlings grew taller as the amount of light increased." Evidence: "Seedlings reached 4 cm in low light, 7 cm in medium light and 11 cm in bright light." Reasoning: "Because the height rose each time the light increased, and light was the only thing changed, the data supports the claim that more light led to taller seedlings in this test." Notice how the claim names the trend, the evidence gives the actual numbers, and the reasoning ties them together while staying inside what was tested.
A weak version of the same conclusion would be: "Light is good for plants." It has no evidence and no reasoning, so a reader cannot check it. The strong version names the trend, quotes the heights, and explains the link, which is what makes it a real conclusion rather than a slogan.
Scientists at the CSIRO testing a new crop write conclusions the same way: claim ("variety X yielded more"), evidence (the tonnes-per-hectare figures), and reasoning (how the figures compare under the same conditions). A reviewer can then check every step.
Do not let your reasoning quietly add a cause you did not test. Here you can say more light went with taller seedlings, but you have not proven light is the only possible reason unless every other variable was truly kept the same.
Not all evidence is equally strong. Strong evidence comes from a fair test, uses repeated measurements, and shows a clear pattern. Weak evidence might be a single reading, come from a test where other variables changed too, or show no real pattern. The stronger your evidence, the further your claim can safely go, but only so far. A conclusion overreaches when it claims more than the data shows, for example saying a result is true for everyone, everywhere, forever, after testing it once on one sample.
Good scientists keep their conclusion tied tightly to what they actually measured. From the seedling test you can say "in this test, more light went with taller seedlings". You cannot say "all plants need bright light", because you tested one plant type, in one place, for two weeks. Staying inside your data is not being weak, it is being honest about what the evidence can support.
One student drops a ball three times from 50 cm and gets bounces of 31, 32 and 30 cm. That repeated, consistent reading is strong evidence for the bounce at 50 cm. A single drop measured once, with the ruler held crookedly, would be weak evidence for the same claim.
When health researchers report a new finding, they are careful to say exactly who was studied, "in this group of 200 adults", not "in everyone". Reporters who drop those limits and write "this cures everything" are overreaching the evidence, which is how science gets misreported.
Words like "always", "never", "everyone" and "proves" are warning signs in a conclusion. One investigation rarely proves anything for all cases, so swap those words for what you actually observed in your test.
Before you trust any conclusion, run it through three quick checks. One: does the evidence actually match the claim, are the numbers really pointing the way the claim says? Two: does the reasoning explain the link, or does it just repeat the claim? Three: does the claim stay inside what was tested, or does it leap to "everyone" and "always"? A conclusion that passes all three is well supported.
This same checklist works on other people's claims too, including the ones you see online. When a headline says a food "boosts brain power", ask: what was the evidence, what was the reasoning, and does the claim go further than the data allows? Most exaggerated claims fail check three, they take a small, specific result and stretch it into a sweeping promise.
Claim: "drinking the new sports drink makes you run faster". Evidence: 10 students ran 100 m slightly faster after drinking it. Check three fails if the conclusion becomes "this drink makes everyone faster at every sport", because only one short run, with a small group, was actually tested.
A conclusion can have real evidence and still be unsupported if the reasoning does not connect them, or if it stretches past the test. Strong evidence does not excuse an overreaching claim, both parts have to hold up.
A student tested one fern in low and bright light and concluded: "All houseplants grow faster in bright light." Which single check does this conclusion fail, and why?
How close was your prediction?
Nice, you saw that one fern cannot stand in for all houseplants.
Good to notice, the claim stretched a single result into a rule for every plant.
Speed Round · 6 questions
True or false? Tap as fast as you can. Build a streak.
In CER, the evidence is the specific data from your investigation.
A claim on its own, with no evidence, counts as a conclusion.
Reasoning explains how the evidence supports the claim.
Saying a result is true "for everyone, everywhere" after one small test is overreaching.
"The plants grew well" is strong evidence for a conclusion.
A good conclusion stays inside the conditions that were actually tested.
How are you completing this lesson?
Think back to the bouncing ball at the start: 12 cm, 25 cm and 37 cm from heights of 20, 40 and 60 cm.
Write a supported conclusion using claim, evidence and reasoning, and explain which word in "balls always bounce higher" was overreaching.
Quick Check · 5 questions
Check Your Understanding · 3 questions
1. In your own words, explain the difference between the claim, the evidence and the reasoning in a conclusion.
2. Why is "the plants grew well" weak evidence, while "4 cm, 7 cm and 11 cm" is strong evidence for the same claim?
3. A student tests one type of paper plane once and concludes "longer wings always fly further". Explain why this conclusion overreaches the data.
Show Your Working · 3 questions
SA1. Name the three parts of a CER conclusion, and describe the job of each one in a single sentence.
SA2. Explain what it means for a conclusion to "overreach" the data, and give one example of an overreaching claim from a single small test.
Hint: Think about words like "always" and "everyone".
SA3. Data: a toy car ran for 12 min, 16 min and 21 min on three battery brands tested in the same car. Write a full conclusion using claim, evidence and reasoning, and make sure it does not overreach.
Quick Check
1. B. The evidence is the specific data, the actual measurements collected.
2. C. Reasoning explains how the evidence supports the claim, linking data to answer.
3. D. "Every plant on Earth" stretches a single short test into a rule for all plants.
4. B. Repeated, closely agreeing readings from a fair test are the strongest evidence.
5. A. It states the claim, quotes the times as evidence, explains the link, and stays inside the test.
Show Your Working Model Answers
SA1 (4 marks): Claim, the short statement answering the question [1]. Evidence, the specific data that backs the claim [1]. Reasoning, the explanation of how the evidence supports the claim [1]. Together they form a conclusion you can defend [1].
SA2 (4 marks): Overreaching means claiming more than the data shows [1], such as saying a result is true for everyone or always [1]. Example: testing one drink on one class and concluding "this drink makes everybody run faster at every sport" [1], when only one short run with a small group was measured [1].
SA3 (5 marks): Claim: in this car, the third battery brand ran longest [1]. Evidence: the run times were 12 min, 16 min and 21 min for the three brands [1]. Reasoning: the third brand gave the longest time when tested in the same car, so the data supports it lasting longest here [1]. It does not overreach because it is limited to this car and these brands [1], rather than claiming the brand is best for every device [1].
Claim
Your answer to the question
Evidence
The specific data that backs it
Reasoning
Why the evidence supports the claim
Conclusion
Claim + evidence + reasoning
Overreaching
Claiming more than the data shows
Supported
Stays inside what was tested
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