Generating Data with Precision: a skill companion
A small set of reusable sheets that grow one inquiry skill: choosing an instrument whose resolution suits the size of the change, recording every value to that resolution, logging with a digital tool at even moments, and judging whether a difference is bigger than the spread of repeats. 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 something is measured: cells under the microscope, heart rates, rock samples, ramps and trolleys, salts and reactions. 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 precision sheet whenever students choose equipment, and the logging sheet when a sensor or logger is used.
- 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 chose a suitable tool and read its scale. In Year 8 they match the resolution to the change they expect (the finest step should be about a tenth of the change, or finer), keep every digit the instrument gives, and tell precision (readings that agree, on a fine scale) from accuracy (readings close to the true value). They also ask whether a difference between two results is bigger than the spread of the repeats, before claiming it is real.
Slot the skill into your science lessons
Every measurement in Year 8 is a chance to practise precision. This map shows a measurement in each Year 8 topic, the instrument and resolution it needs, a digital option, and which scaffold to reach for.
| When you teach | A measurement | Instrument and resolution | A digital option | Scaffold |
|---|---|---|---|---|
| Cells: the Basic Units of Life (AC9S8U01) | The length of onion skin cells | A microscope whose field of view is measured with a clear ruler (about 1.6 mm across at ×100) | A phone photo through the eyepiece, to count cells later | Precision sheet |
| Cells, Tissues and Organ Systems (AC9S8U02) | Heart rate before and after exercise | Beats counted for 30 s on a stopwatch, not 10 s (a miscount is multiplied less) | A pulse sensor or fitness watch, checked against a hand count | Precision sheet, then the cards |
| Plate Tectonics (AC9S8U03) | Earthquake depths across a plate boundary | A published data set, copied to the decimal places it gives | A spreadsheet to sort the records by depth | Logging sheet, part A |
| The Rock Cycle (AC9S8U04) | Mass lost by chalk pieces shaken in a jar | An electronic balance reading to 0.01 g, with the pieces dried first | The balance’s tare key, to weigh without the dish | Precision sheet |
| Kinetic and Potential Energy (AC9S8U05) | The speed of a trolley at the foot of a ramp | A 1 m run between two marks, timed to a few hundredths of a second | A phone video played back frame by frame, or a light gate | The mini-lesson, then the precision sheet |
| Elements, Compounds and Mixtures (AC9S8U06) | Mass of salt left when salty water evaporates | An electronic balance reading to 0.01 g; the dish weighed before and after | The balance’s tare key | Precision sheet |
| Physical and Chemical Changes (AC9S8U07) | The temperature change in a reaction | A digital thermometer reading to 0.1 °C | A temperature probe and data logger, one reading every 5 s | Logging sheet |
| Any science topic | Any measurement | The finest step about a tenth of the change, or finer | Any logger, sensor or spreadsheet the class has | Precision sheet 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.
- Record at even moments, to a tenth of a degree: “A dissolving salt warms the water, logged each minute”.
- Repeat, and keep the real spread: “Three repeats of the peak temperature reached”.
- Keep and check an odd reading instead of hiding it: “A logged heating curve: find the careless point”.
How the scaffolds build the skill
The precision sheet matches instruments to the size of a change, records readings to the resolution, and compares a difference with the spread of repeats. The logging sheet plans a sensor run, then reads a real-looking record with one odd value in it. The cards sort habits into more precise, more accurate, and spoiling the data.
The right resolution, every digit, and the spread
A precise measurement uses a scale fine enough for the change you expect, keeps every digit the instrument gives, and is repeated so you can see how much the readings wobble.
A. Match the resolution to the change
Circle the best tool for each job. Its finest step should be about a tenth of the change, or finer.
| See a temperature rise of about 3 °C as a salt dissolves | a thermometer marked every 1 °C | a digital thermometer reading to 0.1 °C | a hand on the side of the beaker |
| Find the mass lost, about 0.4 g, as a tablet fizzes in a cup | kitchen scales reading to 1 g | bathroom scales | an electronic balance reading to 0.01 g |
| Measure how far a ball rolls across the floor, about 2 m | a 30 cm ruler moved along | a 5 m tape measure marked in centimetres | counting footsteps |
| Time a ball falling 1 m, about 0.45 s | a stopwatch started and stopped by hand | a phone video played back frame by frame (30 frames each second) | a sand timer |
B. Record to the resolution
| The instrument shows | I record |
|---|---|
| An electronic balance (0.01 g) shows 2.50 | |
| A thermometer marked every 1 °C: the liquid sits halfway between 23 and 24 | |
| A digital timer shows 0.460 | |
| A ruler marked in millimetres: the end sits 7 mm past the 12 cm mark |
C. Is the difference bigger than the spread?
Find each mean and range. A difference smaller than the spread of the repeats could just be wobble.
| Three repeats (cm) | Mean | Range | Real difference? | |
|---|---|---|---|---|
| Ball A | 152, 149, 155 | |||
| Ball B | 158, 151, 160 |
| Three repeats (°C) | Mean | Range | Real difference? | |
|---|---|---|---|---|
| Salt X | 3.1, 3.3, 3.2 | |||
| Salt Y | 5.8, 6.0, 5.7 |
Logging with a digital tool
A sensor and logger take readings at exact, even moments and never miss one. They still need a plan: what to measure, how often, for how long, and where the sensor sits. And a careless moment still shows up in the record.
A. Plan the run
B. Read a cooling-cup record
A temperature probe sat in a cup of hot water and logged a reading every 30 s for 10 minutes (time in minutes and seconds).
| Time | °C |
|---|---|
| 0:00 | 68.0 |
| 0:30 | 66.6 |
| 1:00 | 65.3 |
| 1:30 | 64.0 |
| 2:00 | 62.8 |
| 2:30 | 61.7 |
| 3:00 | 60.3 |
| Time | °C |
|---|---|
| 3:30 | 59.3 |
| 4:00 | 58.3 |
| 4:30 | 48.1 |
| 5:00 | 56.1 |
| 5:30 | 55.1 |
| 6:00 | 54.1 |
| 6:30 | 53.0 |
| Time | °C |
|---|---|
| 7:00 | 52.1 |
| 7:30 | 51.3 |
| 8:00 | 50.5 |
| 8:30 | 49.5 |
| 9:00 | 48.7 |
| 9:30 | 48.0 |
| 10:00 | 47.3 |
More precise, more accurate, or spoiling the data?
Cut out the cards. Lay down the three grey heading cards, then sort the habits under them. Precise readings agree with each other; accurate readings are close to the true value. On a blank card, write a habit from your own investigation.
Teacher note: the piles are not the same size. The answer sheet lists which card is which, and why.
One swing or ten?
Use this stand-alone lesson to teach the skill on its own, before you fold it into a science topic. A pendulum about 50 cm long takes about 1.4 s for one swing there and back, and a hand on a stopwatch can be 0.2 s out at each end. Pairs time one swing, then ten swings, and find out which way gives readings that agree.
We are learning to
- choose a way of measuring that suits the size of what is measured,
- record every digit an instrument gives, and repeat to see the spread,
- tell precision (readings that agree) from accuracy (readings close to the true value).
Success criteria
- I can explain why timing ten swings gives a more precise time for one swing.
- I can find the range of my repeats and say whether two results really differ.
You need
- for each pair: a piece of string about 60 cm long with a metal washer or a lump of modelling clay tied to one end, sticky tape to fix the other end to the edge of a desk so about 50 cm hangs free, a ruler and a stopwatch (a phone timer is fine),
- the precision sheet (scaffold 1), one per student, and the cards from scaffold 3, one set per table.
Lesson flow (about 30 minutes)
| 5 min | How precise? Show the board (see the box). Ask: “The three peaks are close but not the same. Should we round them all to 30?” |
| 10 min | One swing Pairs pull the washer about 10 cm to the side, let go, and time one swing there and back, three times, recording every digit. Ask: “How far apart are your three times? Where does the wobble come from?” |
| 10 min | Ten swings Now time ten swings, three times, and divide each by ten. Compare the two ranges. Ask: “Why do the ten-swing results agree better, when the hand is just as slow?” |
| 5 min | Sort the cards Tables sort the cards under the three heading cards. Ask: “Card C is about precision. Which card makes a reading more accurate instead?” |
Running it shorter? Stop after the ten swings, and sort the cards in your next science lesson.
Watch for these ideas
- Thinking more digits always means a better reading, even when the stopwatch hand is the weak link.
- Rounding repeats so that they look as if they agree.
- Calling a reading accurate because it agrees with the other repeats.
Make it easier, make it bigger
- Easier: give a table with rows for one swing and ten swings, and columns for trials 1 to 3, the mean and the range.
- Bigger: time twenty swings and decide whether the extra effort makes the result more precise again, and by how much.
Answers and look-fors
The next sheet has the instrument choices, the recorded readings, the means and ranges, the cooling-cup answers, the card key and a quick three-level guide. Timing one swing typically gives a range of about 0.3 s; ten swings divided by ten, about 0.03 s.
Answers and look-fors
Precision sheet
| Job | Best tool | Why |
|---|---|---|
| See a temperature rise of about 3 °C as a salt dissolves | a digital thermometer reading to 0.1 °C | In steps of 0.1 °C the rise is 30 steps; marks 1 °C apart give only 3. |
| Find the mass lost, about 0.4 g, as a tablet fizzes in a cup | an electronic balance reading to 0.01 g | The balance shows the loss as 40 steps; kitchen scales might show no change at all. |
| Measure how far a ball rolls across the floor, about 2 m | a 5 m tape measure marked in centimetres | One tape laid out reads to 1 cm; moving a ruler seven times adds a small slip each time. |
| Time a ball falling 1 m, about 0.45 s | a phone video played back frame by frame (30 frames each second) | Frames are 0.033 s apart; a hand on a stopwatch can be 0.2 s out, almost half the time. |
| An electronic balance (0.01 g) shows 2.50 | 2.50 g: the last zero says the balance reads to hundredths | |
| A thermometer marked every 1 °C: the liquid sits halfway between 23 and 24 | 23.5 °C: read to half the smallest mark | |
| A digital timer shows 0.460 | 0.460 s: keep every digit the timer gives | |
| A ruler marked in millimetres: the end sits 7 mm past the 12 cm mark | 12.7 cm (or 127 mm) | |
Distance rolled by two balls from the same ramp height: Ball A mean 152.0, range 6; Ball B mean 156.3, range 9. The difference (4.3) is smaller than the spread of the repeats, so it could just be wobble: more repeats are needed.
Temperature rise when 5 g of two salts dissolve in 50 mL of water: Salt X mean 3.2, range 0.2; Salt Y mean 5.8, range 0.3. The difference (2.6) is many times the spread of the repeats, so it is real.
Logging sheet
Part B: 21 readings (10 minutes × 60 ÷ 30 + 1, counting the one at 0:00). The odd reading is 48.1 °C at 4:30, well below 58.3 and 56.1 either side: most likely the probe was lifted out into the cooler air for a moment. Keep it in the record, mark it, and write what happened; draw the cooling curve through the other points. The cup cooled 11.9 °C in the first five minutes and 8.8 °C in the last five: it cools more slowly as it nears room temperature. Part A, for example: a temperature probe (°C), one reading every 5 s for 3 minutes = 37 readings, in the middle of the liquid, clear of the sides.
Data habit cards
| Card | Habit | Pile | Why |
|---|---|---|---|
| A | Keep the probe fully in the liquid, away from the side of the beaker. | More accurate | It reads the liquid, not the air or the glass. |
| B | Check that the thermometer reads 0 °C in a cup of ice and water. | More accurate | A check against a known value shows whether the readings are true. |
| C | Time ten swings of the pendulum and divide by ten. | More precise | The reaction-time slip is shared over ten swings, so repeats agree better. |
| D | Delete the reading that looks too high so the graph looks smooth. | Spoils the data | The record is no longer true; keep it, note it and check it. |
| E | Record the balance reading as 2.50 g, not 2.5 g. | More precise | Keeps the hundredths the balance can show. |
| F | Press tare to zero the balance before adding the powder. | More accurate | Removes the mass of the dish from every reading. |
| G | Read the measuring cylinder with your eye level with the bottom of the curved surface. | More accurate | Looking from above or below makes the reading wrong. |
| H | Round every temperature to the nearest whole degree. | Spoils the data | Throws away the tenths the thermometer gave. |
| I | Let the data logger take a reading every 10 seconds. | More precise | Readings at exact, even moments, with none missed. |
| J | Copy another group’s numbers for the trial you missed. | Spoils the data | Those are not your measurements; record the gap honestly. |
| K | Use a thermometer marked in tenths of a degree instead of whole degrees. | More precise | A finer scale shows smaller changes. |
| L | Measure with a 10 mL measuring cylinder instead of a 100 mL beaker. | More precise | Its marks are much closer together. |
A quick three-level guide
| Move | Working towards | At standard | Beyond |
|---|---|---|---|
| Choose and read the instrument | picks a familiar tool whatever the change | picks a tool whose finest step is about a tenth of the change, and records every digit it gives | explains how a coarse scale would hide the change |
| Repeat and judge the spread | measures once, or rounds repeats to agree | repeats, finds the mean and range, and compares a difference with the spread | tells precision from accuracy and says which a habit improves |
| Log and record honestly | deletes or smooths odd values | plans the interval and number of readings, keeps an odd value and notes it | finds the likely cause of an odd value and plans how to stop it |
A student at standard chooses an instrument to suit the change, records every digit, repeats, and keeps an honest record. The skill grows all year, so keep the scaffolds coming back whenever something is measured.