Validity, Reproducibility and Uncertainty: a skill companion
A small set of reusable sheets that grow one inquiry skill at Year 10 depth: finding the assumption a conclusion quietly rests on, deciding whether a difference is real or sits inside the uncertainty, spotting a hidden change that makes a real difference mean something else, and sorting claims into supported, over-claimed and undecided. Print the scaffolds once and slot them into the lessons you teach.
What a skill companion is
Inquiry skills are not a topic of their own. They grow inside the units a class teaches all year. 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 gives a conclusion, its assumption, the uncertainty and a check for each Year 10 topic.
- Print the assumption sheet when a class writes conclusions, and the difference sheet when it compares two conditions.
- Cut out the cards once. They are reused all year.
- 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 9
The descriptor is the same in Years 9 and 10; the depth is not. In Year 9 students checked a claim and weighed two studies that disagreed. In Year 10 they name the hidden assumption under a conclusion and the check that would test it, judge a difference against its uncertainty before calling it real, and tell a real difference from one caused by something else that changed.
Slot the skill into your science lessons
Every conclusion rests on assumptions and comes with some uncertainty. This map gives, for each Year 10 topic, a conclusion a class might draw, what it assumes, where it is uncertain, and the check that would settle it.
| When you teach | The conclusion | Assumption and uncertainty | The check |
|---|---|---|---|
| Heredity: Cell Division and Inheritance (AC9S10U01) | Both parents were heterozygous | Assumes purple is dominant and the count is fair; a small sample can drift from 3 : 1 | Count more offspring; do a test cross |
| Evolution by Natural Selection (AC9S10U02) | Dark beetles survive better on dark bark | Assumes the “birds” hunted fairly; a single hunt is a small sample | Repeat with different hunters and backgrounds |
| The Big Bang and the Universe (AC9S10U03) | This galaxy is moving away | Assumes the lines are matched correctly and the shift comes from motion | Match several lines; compare many galaxies |
| Energy Flow and Climate Change (AC9S10U04) | The carbon dioxide bottle warmed more | Assumes equal start temperatures and lamp distances; a small gap may sit inside the scatter | Swap the bottles; repeat; compare ranges |
| Newton’s Laws of Motion (AC9S10U05) | a = F ÷ m holds for the trolley | Assumes the force stayed the same and friction was small | Measure the force each run; tilt the track |
| Atomic Structure and the Periodic Table (AC9S10U06) | The flame colour shows the metal | Assumes the splint was clean; a trace of sodium hides other colours | A fresh splint each time; look through a spectroscope |
| Reaction Types and Rates (AC9S10U07) | Smaller chips react faster | Assumes nothing else changed, such as the acid’s temperature | Keep the acid at one temperature; repeat |
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.
- Separate the valid finding from the over-claim: “Which evidence actually supports the claim?”.
- Let the raw repeats expose a method flaw: “Spot the run that exposes a method flaw”.
- Tighten the method rather than defend the result: “How should the method be tightened?”.
What does the conclusion quietly assume?
A conclusion is only as good as the things it takes for granted. For each one, name the assumption that, if it were false, would make the conclusion fall, and the check that would test it. The first is done for you.
| Conclusion | It assumes | The check |
|---|---|---|
| Newton’s Laws of Motion. When we added a second 1 kg trolley, the acceleration halved, so a = F ÷ m holds. | The pulling force stayed the same, and friction was small or the same in both runs. | Measure the force with a force meter in both runs; tilt the track to make up for friction. |
| Energy Flow and Climate Change. The bottle filled with carbon dioxide warmed more under the lamp, so carbon dioxide traps heat. | ||
| Heredity: Cell Division and Inheritance. Our corn cob had 3.1 purple kernels for every yellow one, so both parent plants carried one purple and one yellow allele. | ||
| The Big Bang and the Universe. The lines in this galaxy’s light are shifted towards the red, so it is moving away from us. |
Teacher note: there is usually more than one assumption. Accept any that would sink the conclusion if it were false.
Is the difference real, and does it mean what it seems?
Each comparison gives two means, each ± half the range of its repeats. First, is the difference bigger than the uncertainty: do the two ranges overlap? Then, if it is, did anything else change between the two conditions? Only a clear difference with nothing else changed supports the claim.
Teacher note: a clear difference can still be the wrong cause. A confound is a second change that could explain the same result.
Supported, over-claimed, or undecided?
Cut out the cards. Lay down the three grey heading cards, then sort the claims under them. On the blank cards, write a claim from your own investigation for each heading.
Teacher note: the piles are not the same size. The answer sheet lists which card is which, and why.
Does salt make ice melt faster?
A common claim: sprinkle salt on ice and it melts faster. Pairs test it with two ice cubes on two saucers, salt on one. The result looks simple, but the conclusion rests on assumptions (the cubes were the same size and temperature, the saucers the same), and a small difference may sit inside the scatter of the repeats. When pairs disagree, the class weighs their methods before deciding.
We are learning to
- name the assumptions a conclusion depends on,
- judge a difference against the scatter of the repeats,
- weigh results that conflict by comparing the methods behind them.
Success criteria
- I can list two assumptions under “salt makes ice melt faster” and how I checked them.
- I can say whether our difference was bigger than our scatter, and what the class result shows.
You need
- for each pair: four ice cubes from the same tray, two matching saucers, a teaspoon of table salt, a timer, and a small measuring cylinder,
- the assumption and difference sheets (scaffolds 1 and 2), and the cards from scaffold 3, one set per table. Wipe up meltwater: slippery floors.
Lesson flow (about 30 minutes)
| 5 min | The claim and its assumptions Pairs write the claim, then two things that must be true for their test to be fair. Ask: “If one cube is bigger, what happens to our conclusion?” |
| 12 min | Test it twice Pairs put a cube on each saucer, salt one, and after 8 minutes pour off and measure the meltwater from each; then repeat with fresh cubes. Show the board (see the box) while they wait. Ask: “Your two salted cubes gave different amounts. How big is that scatter next to the salt’s effect?” |
| 8 min | Weigh the class Pairs put their results on the board. If some found no difference, the class compares methods. While they compare, tables sort the claim cards. Ask: “Two pairs disagree. Whose method would you trust more, and why?” |
| 5 min | Write the conclusion Pairs write one conclusion that names the conditions, the uncertainty and one assumption still unchecked. |
Running it shorter? Stop after the first test, and repeat it and weigh the class in your next science lesson.
Watch for these ideas
- Calling any difference a result, however small next to the scatter.
- Siding with the result you expected when two groups disagree, instead of with the better method.
- A conclusion with no conditions: it is true here, for these cubes, at this temperature.
Make it easier, make it bigger
- Easier: give pairs a results table with columns for each cube, the meltwater, and the difference.
- Bigger: try sugar as well as salt, at the same mass. Predict first: if salt works by dissolving, should sugar work too?
Answers and look-fors
The next sheet has the assumptions and checks, the three comparisons worked, the card key, and a quick three-level guide.
Answers and look-fors
Assumption finder (rows 2 to 4)
| Topic | It assumes | The check |
|---|---|---|
| Energy Flow and Climate Change | Both bottles started at the same temperature and sat the same distance from the lamp, and the reaction that made the carbon dioxide did not leave the bottle warmer or wetter. | Start both bottles at room temperature, swap their places, and fill the carbon dioxide bottle a while before the test so any warmth from the reaction has gone. |
| Heredity: Cell Division and Inheritance | Purple is the dominant colour, every kernel was counted once, and the cob came from a single cross of two such plants. | Count a second cob from the same cross, and use a test cross of a purple plant with a yellow one. |
| The Big Bang and the Universe | The lines were matched to the right element, and the shift comes from the galaxy moving away, not from something else such as strong gravity. | Match several lines from the same element, and compare with many galaxies at known distances. |
Is the difference real?
1. carbon dioxide bottle 2.9 to 3.9; air bottle 2.1 to 3.1: they overlap. The ranges overlap, so the difference sits inside the uncertainty: not yet supported. More runs, or a longer warming time, could settle it.
2. 1 kg trolley 1.93 to 2.03; 1.5 kg trolley 1.28 to 1.36: no overlap. The ranges are far apart and only the mass changed: supported, for this force and track.
3. powder 1.7 to 1.9; large chips 0.5 to 0.7: no overlap. The ranges are far apart, but the acid temperature changed too, so the faster rate could come from the warmer acid: the claim is not supported by this test.
Claim cards
| Card | Claim | Pile | Why |
|---|---|---|---|
| A | Our one class found smaller chips react faster, so this is true for every reaction. | Over-claim | One reaction cannot speak for every reaction. |
| B | Two classes found opposite results for the bottles, and neither recorded the start temperature. | Undecided | Conflicting evidence and a missing record: test again. |
| C | Across five runs at each force, the trolley’s acceleration rose in step with the force. | Supported | Repeated, controlled, and stated for the range tested. |
| D | Warmer acid dissolved the ribbon faster at every temperature from 20 to 50 °C, in three classes. | Supported | Replicated across classes, within the range tested. |
| E | The line through our results shows the ribbon would dissolve instantly at 150 °C. | Over-claim | Far outside the range tested, and the acid would boil. |
| F | Dark paper beetles survived the hunt better on dark bark, so dark beetles evolved because they wanted to hide. | Over-claim | Selection does not need wanting; and one model hunt is not evolution. |
| G | The salted ice melted 4 s sooner, but repeats varied by 20 s. | Undecided | The difference is far smaller than the scatter. |
| H | Of 400 seedlings from a Tt × Tt cross, 297 were tall, close to three in four. | Supported | A large sample, close to the predicted ratio. |
| I | The bottle with more carbon dioxide warmed more, so carbon dioxide alone controls Earth’s climate. | Over-claim | A bottle cannot show what alone controls a planet. |
| J | Every galaxy in our class data set with a larger distance had a larger red shift. | Supported | A consistent pattern, stated for the data set. |
| K | One survey found students who sleep more score higher; a second, larger one found no link. | Undecided | Conflicting studies: weigh their methods before deciding. |
| L | Lithium reacted with water, so potassium will react exactly the same way. | Over-claim | Same group, but the trend says potassium reacts faster. |
A quick three-level guide
| Move | Working towards | At standard | Beyond |
|---|---|---|---|
| Assumptions | takes the conclusion at face value | names an assumption that would sink it, and a check | designs the check and says what result would change the conclusion |
| Uncertainty | calls any difference a result | compares a difference with the uncertainty of the repeats | says how many more repeats would settle an undecided case |
| Conflicting evidence | sides with the expected result | compares the methods behind conflicting results | finds the confound that explains a clear but misleading difference |
In the mini-lesson, salted cubes usually give clearly more meltwater, because dissolved salt lowers the temperature at which water freezes. Pairs that found no difference often had cubes of different sizes. Sugar works too, but far less for the same mass: it makes fewer dissolved particles.