Evaluating Methods and Claims: a skill companion
A small set of reusable sheets that grow one inquiry skill: taking a method, a conclusion or a claim apart to find its assumptions, its possible sources of error, the evidence that conflicts with it and the questions it leaves open. Students also tell systematic error from random error and from a plain mistake, and choose the fix that suits each. Print the scaffolds once and slot them into the science lessons you already teach.
What a skill companion is
Inquiry skills are not a topic of their own. They grow inside the science units a class teaches all year, wherever a conclusion is drawn or a claim is made: about cells, heart rates, earthquakes, rocks, bounces, salts and reactions, and in the headlines and videos students meet every day. So this pack is not a full term of lessons. It is three reusable scaffolds, a map of where they fit, and a short stand-alone lesson for teaching the skill on its own first.
Start here: five minutes
- Read the pairing map on the next page: it shows which scaffold fits which science lesson.
- Print the claim checker whenever a conclusion or headline needs testing, and the error sheet after any practical.
- Cut out the cards once. They are reused all year, and the blank cards fit any topic.
- Open the free interactive unit on your board when you want a worked example of the skill.
- Run the one-page mini-lesson first if you want to teach the skill before folding it into a topic.
The step up from Year 7
In Year 7 students checked a class report for weaknesses and explained why two groups disagreed. In Year 8 they test claims from outside the classroom as well, weigh the size and design of the evidence against a conflicting test, and sort errors by what they do: a systematic error shifts every reading the same way and needs correcting or calibrating, a random error scatters readings and needs repeats, and a mistake is a one-off slip to redo. They also find that a systematic error barely changes a difference between readings.
Slot the skill into your science lessons
Every conclusion in Year 8 can be tested the same way. This map shows a claim or conclusion in each Year 8 topic, an assumption or error to look for, a question it leaves open, and which scaffold to reach for.
| When you teach | A claim or conclusion | An assumption or error to look for | A question it leaves open | Scaffold |
|---|---|---|---|---|
| Cells: the Basic Units of Life (AC9S8U01) | “Onion cells are all the same size”, from one slide | Assumes one slide stands for the whole onion; cells measured at different angles | Do cells from the root and the leaf differ? | Claim checker |
| Cells, Tissues and Organ Systems (AC9S8U02) | “Exercise doubles everyone’s heart rate” | Assumes everyone worked equally hard; a 10 s count multiplied by 6 magnifies a miscount | Does fitness change how fast the rate recovers? | Claim checker, then the cards |
| Plate Tectonics (AC9S8U03) | “Earthquakes are getting more common”, from a headline | Assumes small earthquakes were always recorded as well as they are now, with far more instruments | Are large earthquakes more common, or just better recorded? | Claim checker |
| The Rock Cycle (AC9S8U04) | “Longer shaking always rounds rock faster” | Wet chalk weighs more: a systematic error if every piece is weighed wet | Does hard rock round as fast as chalk? | Error sheet |
| Kinetic and Potential Energy (AC9S8U05) | “A heavier ball always bounces higher” | Assumes the same material; reading every bounce from above the top of the ball | Does the floor matter more than the ball? | Error sheet, then the cards |
| Elements, Compounds and Mixtures (AC9S8U06) | “We got back all the salt we dissolved” | Salt left on the filter paper; a splash from the evaporating dish | How much salt was lost, and where? | Error sheet |
| Physical and Chemical Changes (AC9S8U07) | “Fizzing always means a chemical change” | Assumes gas means a new substance, but opening a fizzy drink releases gas with no reaction | Which signs show a new substance for sure? | The mini-lesson, then the claim checker |
| Any science topic | Any claim, conclusion or headline | Assumptions, errors and conflicting evidence | What would a better test need? | Claim checker first |
The three moves, and the picture that backs each one
When you want a worked example on the board, open the interactive unit and use the picture that matches the move.
- Keep the finding inside the data: “Sound conclusion, or an over-claim?”.
- Find the source of error hiding in the raw data: “Spot the reading that exposes a method flaw”.
- Weigh what each fix costs and what it removes: “How should the method be fixed?”.
How the scaffolds build the skill
The claim checker takes a claim, its evidence and a conflicting test through six questions to a verdict. The error sheet finds a systematic error in a balance and a thermometer by checking each against a known value, and matches fixes to the errors they reduce. The cards sort situations into systematic error, random error and mistakes.
Check a claim before you believe it
A claim is only as strong as the evidence behind it. Find what is claimed, what the evidence was, what it assumes, what could have gone wrong, what disagrees with it, and what nobody has answered yet. Then decide.
| What exactly is claimed? | |
|---|---|
| What evidence is given, and how big is the sample? | |
| Two assumptions the evidence relies on | |
| A possible source of error | |
| How is the other test different, and which is stronger? | |
| A question still unanswered |
My verdict
Systematic error, random error
A systematic error pushes every reading the same way, so repeating does not show it: you find it by checking against a known value. A random error scatters readings a little either way, so repeats show it and a mean reduces it.
A. A balance and five coins
Before weighing, the balance read 0.30 g with nothing on it, and nobody pressed tare. Five 5-cent coins were weighed one at a time. A 5-cent coin has a mass of 2.83 g.
| Coin | 1 | 2 | 3 | 4 | 5 |
|---|---|---|---|---|---|
| Reading (g) | 3.12 | 3.14 | 3.13 | 3.11 | 3.14 |
B. Two thermometers in one cup
| Time (min) | 0 | 2 | 4 | 6 | In ice and water |
|---|---|---|---|---|---|
| Thermometer A (°C) | 62.1 | 55.0 | 49.3 | 44.8 | 2.0 |
| Thermometer B (°C) | 60.0 | 53.1 | 47.2 | 42.9 | 0.1 |
C. Which error does each fix reduce?
| Fix | Systematic or random? |
|---|---|
| Repeat the measurement and take the mean | |
| Press tare, or subtract the reading with nothing on the balance | |
| Check against a known value, such as ice and water, and correct | |
| Read the scale with your eye level with the mark | |
| Time ten swings instead of one |
Systematic, random, or a mistake?
Cut out the cards. Lay down the three grey heading cards, then sort the situations under them. Ask: would every reading be off the same way, would readings scatter both ways, or is it a one-off slip?
Teacher note: the piles are not the same size. The answer sheet lists which card is which, and why.
The width of a sheet of paper
Use this stand-alone lesson to teach the skill on its own, before you fold it into a science topic. Every student measures the width of a sheet of A4 paper, which is 210 mm by definition. Against a value the class knows, ordinary scatter, a systematic error and a mistake all show up on one dot plot.
We are learning to
- tell systematic error, random error and a mistake apart, and choose a fix for each,
- find the assumptions behind a measurement or a claim,
- treat results that disagree as evidence to explain, not a contest to win.
Success criteria
- I can point to the scatter, the systematic error and the mistake on the class dot plot.
- I can say which fix suits each one.
You need
- a sheet of A4 paper and a 30 cm ruler for each student (collect a few rulers with a gap before the 0 mark and a few with a worn end), a dot plot on the board from 200 to 300 mm,
- the error sheet (scaffold 2), one per student, and the cards from scaffold 3, one set per table.
Lesson flow (about 30 minutes)
| 5 min | A flaw in the method Show the board (see the box). Ask: “The bath was set to 40 degrees. Why was the run not really at 40?” |
| 10 min | Measure and plot Without discussion, each student measures the width of the A4 sheet to the nearest millimetre and adds a dot to the board. Ask: “Most dots sit near one value. What makes them spread a little?” |
| 10 min | Explain the odd ones Reveal that A4 is 210 mm wide. Pairs explain any group of dots that sits a few millimetres off, and any single dot far away. Ask: “Several dots read 205. What do their rulers have in common?” |
| 5 min | Sort the cards Tables sort the cards under the three heading cards. Ask: “Card E is systematic. Why would repeating that weighing ten times not fix it?” |
Running it shorter? Stop after explaining the dot plot, and sort the cards in your next science lesson.
Watch for these ideas
- Thinking that repeating a measurement removes every kind of error.
- Calling every odd reading an error, when it may be a one-off mistake.
- Trusting whichever result came from the bigger group, without comparing the methods.
Make it easier, make it bigger
- Easier: give the three headings on the board beside the dot plot, and sort the dots under them together.
- Bigger: measure the length of the sheet too (297 mm) and check whether the same rulers are off by the same amount.
Answers and look-fors
The next sheet has the claim checker answers, the coin and thermometer working, the fixes, the card key and a quick three-level guide. Typical dot plot: most dots from 209 to 211 mm (random scatter), a cluster near 205 or 215 mm from rulers read from the end rather than the 0 mark (systematic), and sometimes a dot near 297 mm from measuring the length (a mistake).
Answers and look-fors
Claim checker
| What exactly is claimed? | A magnet on the fuel line cuts petrol use by 20%. |
|---|---|
| The evidence, and its size | One car, one driver, one month with the magnet against one month without; fuel judged by how often the tank was filled. |
| Two assumptions | That the two months were the same in distance, traffic, weather and driving; and that filling up less often means using less fuel. |
| A possible source of error | Filling to different levels each time, so the number of fill-ups is a rough measure of fuel used. |
| The other test | Twenty cars, the same route both ways, fuel measured by filling to the brim: a larger, fairer test, and it found no real difference. |
| A question still unanswered | How could a magnet change petrol at all? What else changed in the presenter’s second month? |
Verdict: not supported. One car over two different months cannot show a 20% saving, and the larger, fairer test found less than 1% difference either way. A fair test needs many cars, the same route and driving, fuel measured exactly, and each car tested both ways.
Error sheet
A. Mean reading 3.13 g, 0.30 g above the true 2.83 g: the 0.30 g zero error, a systematic error that is in every reading. The readings scatter over only 0.03 g: random error. Corrected mean 3.13 − 0.30 = 2.83 g.
B. Thermometer A reads about 2 °C high: in ice and water it shows 2.0 °C instead of 0, and it is about 2 °C above B all the way. Drops over 6 minutes: A 17.3 °C, B 17.1 °C. They agree because the same offset is in both readings of each drop and cancels when one is taken from the other.
C. Repeat the measurement and take the mean: random; Press tare, or subtract the reading with nothing on the balance: systematic; Check against a known value, such as ice and water, and correct: systematic; Read the scale with your eye level with the mark: systematic; Time ten swings instead of one: random.
Error cards
| Card | Situation | Pile | Why |
|---|---|---|---|
| A | A draught makes the balance reading flicker between 2.81 and 2.85 g. | Random error | Readings wander either way; shield the balance and average. |
| B | Pulse counts wobble by a beat or two from one count to the next. | Random error | Scatter both ways; count for longer or repeat. |
| C | The ruler’s end is worn, and every length is measured from the end, not the 0 mark. | Systematic error | Every length comes out short by the same amount. |
| D | Each person reading the ruler lines it up by eye a little differently. | Random error | Small differences in both directions. |
| E | The balance shows 0.30 g with nothing on it, and nobody presses tare. | Systematic error | Every mass is 0.30 g too high. |
| F | The tablet for the 40 °C run was dropped into the 20 °C cup. | Mistake | A one-off slip; redo that run. |
| G | The thermometer reads 2 °C high, even in a cup of ice and water. | Systematic error | Every temperature is 2 °C too high; correct it. |
| H | The stopwatch is started on hearing a clap from across the oval, not on seeing it. | Systematic error | Sound takes time to arrive, so every start is late by the same amount. |
| I | Reaction time makes each stopwatch time a little early or a little late. | Random error | Either way, by different amounts; repeat and average. |
| J | Every reading of the measuring cylinder is taken from above the liquid. | Systematic error | Looking from above always misreads the same way. |
| K | One trial was written in the wrong row of the table. | Mistake | A slip in recording; check and correct it. |
| L | Some water spilled from the beaker before it was weighed. | Mistake | A one-off loss; repeat that trial. |
A quick three-level guide
| Move | Working towards | At standard | Beyond |
|---|---|---|---|
| Test a claim | accepts or rejects it on feeling | names the evidence, its size, an assumption and a source of error, and reaches a verdict | designs a fair test that would settle the claim |
| Weigh conflicting evidence | picks the result they prefer | compares the two methods and says which test is stronger | explains how the difference in method could produce the disagreement |
| Sort and fix errors | calls every problem an error, and repeats to fix it | tells systematic error, random error and a mistake apart, with a fix for each | shows that a constant offset barely changes a difference between readings |
A student at standard tests a claim against its evidence, compares conflicting tests by their methods, and sorts errors by what they do. The skill grows all year, so keep the scaffolds coming back whenever a conclusion is drawn.