Topics · Primary Science · Process Skills: Fair Test & Variables
Fair tests and variables
A fair test changes one thing, keeps everything else the same, and measures what happens. If two things changed at once, the experiment cannot tell you which one caused the result — and that is the whole idea being examined.
- 535 exam papers analysed
- appears in 100% of P6 Science papers
- ~4 min read
01 The three kinds of variable
Every fair test has exactly three roles, and naming them correctly is most of the marks.
Changed — the one thing you deliberately make different between the set-ups. There must be only one.
Measured — what you observe or record to see the effect. This is the result.
Kept the same — everything else. The longer the list you can give, the better the answer.
02 Reading a set-up
Papers give you two or more set-ups and ask which variable is which. Compare them item by item, and the one that differs is the changed variable.
In the pair above: the changed variable is the water temperature; the measured variable is how long the sugar takes to dissolve; the variables kept the same include the volume of water, the size of the sugar cube, the type of sugar and whether it was stirred.
If more than one thing differs, it is not a fair test. That is the answer papers want when they show you a bad set-up, and saying only “it is not fair” without naming the second difference does not score.
03 Writing the answer they want
The wording is marked as closely as the science. These four habits carry most of the marks.
- Name the variable, do not just point. “The temperature of the water” scores; “the temperature” or “the heat” often does not.
- One changed variable only. If you find yourself naming two, the set-up is unfair and that is the answer.
- Give more than one thing kept the same when asked. A single item rarely gets the full mark.
- Say what you measured and how. “How long the sugar took to dissolve, in seconds” beats “what happened”.
- Repeat readings to check the result. A question about improving an experiment usually wants this.
| Water temperature | Time to dissolve (s) |
|---|---|
| 30 °C | 95 |
| 45 °C | 60 |
| 60 °C | 38 |
04 Conclusions, and what they may not say
A conclusion links the changed variable to the measured one: the hotter the water, the faster the sugar dissolved. Nothing more.
It may not wander outside what was tested. This experiment says nothing about salt, nothing about water above 60 °C, and nothing about stirring — none of those were changed.
A pattern is not automatically a cause. It is a cause here only because everything else was held still, which is exactly what made the test fair. That is why the fairness matters and not just the result.
05 How to say them
These are words most children have never said out loud, and a word you cannot say is a word you avoid using. Capitals mark the syllable you lean on. Tap the speaker to hear it.
- variablesayVAIR-ee-uh-buhlmore than onevariables
Anything in an experiment that could change: what you change, what you measure, and what you keep the same.
- fair testmore than onefair tests
An experiment where only one variable is changed and all the others are kept the same.
- independent variablesayin-di-PEN-duhnt
The one thing you deliberately change. Papers often just say “the variable changed”.
- dependent variablesaydi-PEN-duhnt
The thing you measure, which depends on what you changed.
- constantsayKON-stuhntmore than oneconstants
A variable kept the same on purpose, so it cannot affect the result.
- conclusionsaykuhn-KLOO-zhuhnmore than oneconclusions
What the results show, stated as a link between the changed variable and the measured one.
- predictionsaypri-DIK-shuhnmore than onepredictions
What you expect to happen before you do the experiment.
06 What each level is tested on
The same topic, asked differently as it goes up. The percentage is the share of papers at that level in which it appears.
- P3
Spotting what was changed and what was kept the same in a simple set-up.
Practise P3 Process Skills: Fair Test & Variables — 10 questions →72% of P3 papers
- P4
Naming all three kinds of variable, and saying why a test is not fair.
Practise P4 Process Skills: Fair Test & Variables — 10 questions →95% of P4 papers
- P5
Reading results tables and graphs, and writing a conclusion that does not overreach.
Practise P5 Process Skills: Fair Test & Variables — 10 questions →91% of P5 papers
- P6
Planning an experiment, judging someone else's, and suggesting improvements. Marked in every P6 paper.
Practise P6 Process Skills: Fair Test & Variables — 10 questions →100% of P6 papers
07 Mistakes worth knowing about
Each of these is wrong. Decide why before you open it.
“It is not a fair test.”
True but not enough. Name the second thing that differed — that is where the mark is.
“The variable changed was the heat.”
Too vague. “The temperature of the water” names it; “heat” and “temperature” are different things in Science.
“Everything else was kept the same.”
List them. Volume of water, mass of sugar, size of the cube, whether it was stirred. A blanket phrase usually scores nothing.
“The hotter the water, the faster things dissolve.”
Only sugar was tested. Say “the sugar dissolved faster”, and do not extend the conclusion past what was changed.
“I only did it once, but the result was clear.”
One reading could be a fluke. Repeating and taking an average is the standard answer to “how could this experiment be improved”.
Now try it
40 questions across 4 levels, marked as you go with the working shown.