Valid, Reproducible Investigations: a skill companion
A small set of reusable sheets that grow one inquiry skill at Year 10 depth: planning an investigation whose results are valid and can be reproduced, telling systematic error from random error and from plain mistakes, and writing and following a risk assessment, with ethics and heritage on Country and Place in view. Print the scaffolds once and slot them into the lessons you already 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 the hazard, the control and the record for a practical in each Year 10 topic.
- Print the risk assessment before any practical, and the error hunt when a class has two sets of results that disagree.
- 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 wrote a method another group could follow. In Year 10 they also name the kind of each error and the fix that suits it (repeats reduce random error but never systematic error), write the risk assessment themselves, and judge a result against a prediction to find a hidden systematic error.
Slot the skill into your science lessons
Every practical asks the same questions: what could hurt someone, what must stay the same for the result to be valid, and what must be written down for another class to reproduce it? This map answers them for one practical in each Year 10 topic.
| When you teach | The practical | Main hazard and control | Keep it valid | Record to reproduce |
|---|---|---|---|---|
| Heredity: Cell Division and Inheritance (AC9S10U01) | Count purple and yellow kernels on a genetics corn cob | Low: wash hands after handling; nothing eaten | Count every kernel in marked rows; two counters agree | The cob’s label and the counting rule |
| Evolution by Natural Selection (AC9S10U02) | Paper “beetles” of two colours hunted on a background | Scissors; no live animals are needed for the model | Same number of each colour, same time limit for each hunt | Background, colours, numbers and rounds |
| The Big Bang and the Universe (AC9S10U03) | Dots on a balloon as it is blown up | A latex allergy; a burst near eyes: use a pump and latex-free balloons if needed | Measure every distance at the same stage of inflation | Pump strokes at each stage; how distances were measured |
| Energy Flow and Climate Change (AC9S10U04) | Two bottles warming under a lamp | Hot lamp, glass: plastic bottles, lamp clamped away from hands | Same bottle, start temperature, distance and lamp | Lamp power, distance, times of every reading |
| Newton’s Laws of Motion (AC9S10U05) | Trolley acceleration at a fixed force | Falling trolley or masses: clamp the ramp, padded stop | Track tilted to make up for friction; same release | Track angle, masses, timing method, every run |
| Atomic Structure and the Periodic Table (AC9S10U06) | Flame colours of metal salts | Burns, some toxic salts: teacher-chosen salts, demonstration or close supervision | A clean splint for each salt | Salt, solution strength, flame setting |
| Reaction Types and Rates (AC9S10U07) | Marble chips in dilute acid | Acid splashes, gas: glasses, small volumes, ventilation | Same mass and size of chips, same acid volume and strength | Chip source and size, acid strength, every reading |
Fieldwork on Country or Place, in any unit: ask permission first, leave rock art, stone arrangements, scarred trees and artefacts undisturbed, and seek guidance from the Traditional Owners before going further.
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.
- Control what could confound the result: “Control the confounds so the force test is valid”.
- Choose enough repeats, and stop by a rule, not by the answer: “Choose how many runs to time at each force setting”.
- Check the whole plan, safety and heritage included: “Judge the plan for the force-and-acceleration investigation”.
What could go wrong, and what will we do?
A risk assessment names each hazard, the control that makes it unlikely or less harmful, and what to do if it happens anyway. Write it before the practical, and follow it during. The first row is done for you.
| Practical | Hazard: what could hurt someone | Control | If it happens |
|---|---|---|---|
| Magnesium ribbon in warm dilute hydrochloric acid (rates) | Acid splashing into eyes or onto skin; flammable hydrogen gas | Safety glasses; dilute acid only, warmed in a water bath no hotter than 50 °C; small volumes; no flames nearby | Rinse under running water for 15 minutes (eyes at the eyewash) and tell the teacher |
| A trolley pulled along a ramp, with masses added (Newton’s laws) | |||
| Two bottles warming under a heat lamp (greenhouse model) | |||
| Flame tests with wooden splints soaked in salt solutions (atoms) |
My own investigation
Teacher note: check and sign each pair’s risk assessment before the equipment comes out.
Two groups, two kinds of error
Two groups pulled a 1 kg trolley with a 2 N force, five runs each. With no friction, Newton’s second law predicts an acceleration of 2 m/s². Group A ran on a level track. Group B tilted the track to make up for friction but timed each run by hand.
| Acceleration (m/s²) | Run 1 | Run 2 | Run 3 | Run 4 | Run 5 | Mean | Range |
|---|---|---|---|---|---|---|---|
| Group A | 1.62 | 1.60 | 1.63 | 1.61 | 1.62 | ||
| Group B | 1.75 | 2.28 | 1.92 | 2.15 | 1.85 |
A. Read the results
B. Name the errors
C. Fix the method
Systematic error, random error, or a mistake?
Cut out the cards. Lay down the three grey heading cards, then sort the problems under them. On the blank cards, write a problem from your own investigation for each heading, and the fix that suits it.
Teacher note: the piles are not the same size. The answer sheet lists which card is which, and the fix for each.
Can another pair get our result?
A marble rolls down a grooved ruler propped on books and pushes a paper cup, lying on its side, along the desk. The higher the ramp, the further the cup slides. Each pair writes a risk assessment, measures the slide at three heights, and then hands its method to another pair to reproduce. Where the two disagree, the class hunts for the error and names its kind.
We are learning to
- write and follow a short risk assessment,
- control the variables that would make a result invalid,
- tell a systematic error from a random one, and fix each the right way.
Success criteria
- I can name two hazards in this practical and the control for each.
- I can say whether another pair reproduced our result, and which kind of error explains any difference.
You need
- for each pair: a 30 cm ruler with a groove, a marble, three books of equal thickness, a paper cup, a second ruler, and a book or box as a wall at the end of the desk,
- the risk assessment and error hunt (scaffolds 1 and 2), and the cards from scaffold 3, one set per table. Count the marbles out and back in.
Lesson flow (about 30 minutes)
| 5 min | Risk first Pairs write two hazards and a control for each on scaffold 1 before touching the equipment. Ask: “A marble on the floor is a hazard to whom? What control stops it getting there?” |
| 12 min | Measure Pairs measure the slide of the cup at ramp heights of one, two and three books, three runs each, and write a method on one card. Show the board (see the box). Ask: “What must stay the same so that only the ramp height changes the slide?” |
| 8 min | Swap and reproduce Pairs swap method cards and repeat each other’s middle height. While they compare, tables sort the error cards. Ask: “Your slide is always shorter than theirs. Is that random or systematic? What could cause it?” |
| 5 min | Fix the method Each pair adds one line to its method that would have made the result easier to reproduce, such as where the cup starts. |
Running it shorter? Stop after the measurements, and run the swap in your next science lesson.
Watch for these ideas
- Thinking more runs fix every error: they shrink random error but leave a systematic one untouched.
- Calling a slip, such as a misread ruler, “human error” and keeping the reading.
- A risk assessment written after the practical, or not followed during it.
Make it easier, make it bigger
- Easier: give pairs a method with blanks for the ramp height, the cup’s start line and the number of runs.
- Bigger: swap the paper cup for a heavier one without telling the other pair. Can they find the systematic error from the results alone?
Answers and look-fors
The next sheet has model risk assessments, the worked error hunt, the card key with a fix for each card, and a quick three-level guide.
Answers and look-fors
Risk assessment (rows 2 to 4)
| Practical | Hazard | Control | If it happens |
|---|---|---|---|
| A trolley pulled along a ramp, with masses added (Newton’s laws) | The trolley or a slotted mass falling off the bench onto feet; fingers caught at the pulley | Clamp the ramp; a padded stop or box at the end; small masses held on with tape; stand clear of the line | Stop the run; first aid for a bruise or crushed finger; report it |
| Two bottles warming under a heat lamp (greenhouse model) | Burns from the hot lamp; a glass bottle breaking | Plastic bottles; the lamp clamped 30 cm away and switched off before moving it; no touching the shade | Cool a burn under running water for 20 minutes and tell the teacher |
| Flame tests with wooden splints soaked in salt solutions (atoms) | Burns from the flame; hair or sleeves catching; some salts are toxic | Teacher demonstration or close supervision; hair tied back; safety glasses; low-hazard salts only, chosen by the teacher; splints dropped into water after use | Cool a burn under running water for 20 minutes; smother a small fire with a fire blanket; tell the teacher |
Error hunt
Group A: mean 1.616 m/s², range 0.03. Group B: mean 1.990 m/s², range 0.53. Group A is more precise but sits well below the prediction of 2 m/s² on every run: a systematic error, friction on the level track. Ten more runs would give the same low mean; tilt the track until the trolley, nudged, rolls at a steady speed, then repeat. Group B is close to the prediction on average but scattered: random error from timing by hand. More runs would steady the mean; light gates or a slow-motion video would shrink the scatter. A third group needs the track tilt (or how friction was made up for), the mass and force, the timing method and the number of runs.
Error cards
| Card | Problem | Pile | Why, and the fix |
|---|---|---|---|
| A | The balance shows 0.3 g before anything is put on it. | Systematic error | Every mass reads 0.3 g too high; tare the balance. |
| B | A result of 1.62 is written in the table as 1.26. | Mistake | A copying slip; check against the raw record. |
| C | A stopwatch is started and stopped by hand. | Random error | Reaction time varies run to run, early or late. |
| D | Draughts in the room change how fast a paper helicopter falls. | Random error | Unpredictable, both ways; repeat and average, or shut the windows. |
| E | The track slopes slightly upward in the direction the trolley moves. | Systematic error | Every acceleration reads low; level or tilt the track to make up for friction. |
| F | The thermometer is always read from above the liquid level. | Systematic error | Parallax shifts every reading the same way; read at eye level. |
| G | One trial uses acid twice as concentrated as the method says. | Mistake | The wrong method was followed; redo that trial. |
| H | A needle wobbles between two marks while it is read. | Random error | Each reading lands a little high or low; take several and average. |
| I | A ruler’s worn end means every length is measured from the 1 cm mark without subtracting it. | Systematic error | Every length is 1 cm too long; subtract it, or use a ruler with a clear zero. |
| J | The trolley is let go a little harder on some runs than others. | Random error | A push that varies scatters the results; release it from rest the same way. |
| K | The light gate is not reset between two runs. | Mistake | That run’s time is wrong; reset and run it again. |
| L | A stopwatch that runs 2% fast is used for every timing. | Systematic error | Every time is 2% too long; check it against a reliable clock. |
A quick three-level guide
| Move | Working towards | At standard | Beyond |
|---|---|---|---|
| Validity | changes more than one thing at a time | controls the variables that could confound the result | finds a hidden systematic error by comparing with a prediction or a standard |
| Reproducibility | writes a method only the writer could follow | records the settings, the method and every reading | reproduces another group’s result and explains any difference |
| Risk and ethics | starts before thinking about hazards | names each hazard with a control and a response | adds ethical and heritage steps without being prompted |
A student at standard controls the confounds, records enough to be reproduced, and names each hazard with its control. In the mini-lesson, the cup slides further from a higher ramp; a pair that cannot reproduce another’s slide usually started the cup in a different place or used a different cup, both systematic.