Science / Year 6 / Working Scientifically / 6.3
Estimated time: 35 minutes | Difficulty: Easy | Ref: KS2-WS-1b
Learning objective: Understand and apply principles of fair testing
Use the pathway to build a clear mental model. Open each node and answer the check question.
A fair test is an investigation where you only change ONE thing (the independent variable) while keeping everything else the same. This way, you can be sure that any changes in your results are caused by the thing you changed, not something else.
Check: If you changed two things at once, why couldn't you trust your results?
Before you begin, ask yourself: What am I changing? (one thing only), What am I measuring? (the dependent variable), What am I keeping the same? (all the control variables). If you can answer all three, you're ready for a fair test!
Check: What three questions should you ask before starting a fair test?
Think about EVERYTHING that could affect your results. For example, in a plant growth experiment: pot size, soil type, water amount, light level, temperature, type of seed, and more must all be kept the same. Miss even one, and your test isn't fair!
Check: What could go wrong if you used different sized pots in a plant experiment?
Practice spotting when a test is NOT fair. Ask: "Did they change more than one thing?" If a student tested a big paper aeroplane made of card against a small one made of tissue paper - that's unfair! They changed both size AND material.
Check: What would make that aeroplane test fair?
A fair test is a controlled experiment where you change only ONE variable (the independent variable) and measure what happens (the dependent variable), while keeping everything else exactly the same (control variables). This is the gold standard of scientific investigation because it allows you to draw valid conclusions.
| Rule | What This Means | Example |
|---|---|---|
| Change only ONE thing | Only the independent variable changes | Only change the ramp height, not the car |
| Measure ONE thing | Measure the dependent variable consistently | Always measure distance in centimetres |
| Keep EVERYTHING else the same | Control all other variables | Same car, same surface, same starting position |
| Repeat for reliability | Do each test at least 3 times | Test each ramp height 3 times, calculate average |
Investigation: Does the type of surface affect how far a marble rolls?
Sometimes a fair test isn't possible. You can't control people's heights to test if taller people run faster - you'd use pattern seeking instead. You can't control the weather to test plant growth outdoors - but you could in a greenhouse! Recognising when fair testing IS and ISN'T appropriate is an important scientific skill.
Without fair testing, we couldn't trust scientific conclusions. Medical researchers must use fair tests when developing new medicines - imagine if they tested a new drug on healthy young people but an old treatment on ill elderly people! The comparison wouldn't be valid. Fair testing is the foundation of reliable science.
Question: Which type of ball bounces highest?
Making it fair:
Scenario: Emma wants to find out if fertiliser helps plants grow taller. She gives Plant A fertiliser and puts it on a sunny windowsill. She gives Plant B no fertiliser and puts it in a shady corner.
Is this fair? NO!
Problem: Emma changed TWO things - the fertiliser AND the light level. If Plant A grows taller, she won't know if it was the fertiliser or the sunlight that caused it!
Fix: Keep both plants in the same location with the same light. Only change whether they receive fertiliser.
Question: Does wing length affect how long a paper helicopter takes to fall?
Fair test setup:
Each wing length tested 3 times. Results averaged. Anomalies identified and noted.
How pharmaceutical companies use fair testing:
When testing a new medicine, scientists must use fair test principles on a huge scale:
This is why we can trust that medicines actually work - they've been fairly tested!
Answer all questions, then check your answers. Your quiz result is saved on this device.
✗ Wrong: "I tested a red car on carpet and a blue car on wood to see which surface has more friction."
✓ Right: "I tested the SAME car on carpet and wood to see which surface has more friction."
If you change the car AND the surface, you can't tell which caused the difference in results!
✗ Wrong: "To make it fair, I used the same beaker." (but forgot about water temperature, stirring, timing...)
✓ Right: "To make it fair, I used: the same beaker, the same volume of water (100ml), the same starting temperature (20°C), the same stirring speed (10 stirs), and the same timing method (stopwatch)."
Think of EVERYTHING that could affect your results and list them all!
✗ Wrong: "I'll do a fair test to see if people with bigger hands can catch a ball better."
✓ Right: "I can't control hand size - I need to use pattern seeking instead, collecting data from different people and looking for a relationship."
Fair tests only work when you CAN control the variables. If you can't, use a different enquiry type!
✗ Wrong: Measuring one ball's bounce by looking down at a ruler, and another by filming it.
✓ Right: Using exactly the same measurement technique for every test - either film them all or measure them all at eye level.
Your method must be identical every time, or you're introducing unfair variation!