ScienceWorking scientifically30 min★★★ difficulty

Planning a fair test

A good investigation answers one question at a time. This lesson is the planning skill assessed in every practical: choosing variables, controlling the rest and making the method repeatable.

Part of your national curriculum

Working scientifically: Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables

Lesson overview

What you'll learn in this lesson

Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables

Key learning points

• One change at a time
• Predictions with reasons
• A method someone else can repeat
• Range, interval and safety

This lesson at a glance

30 minutes
19 parts to scroll through
4 quick checks
Marked quiz at the end
Gentle pace: short sittings with pauses

Words to know

appropriatescientificenquirypredictionsidentifying

Scroll down — the lesson carries on below

Part 1 of 19 · Discover5%

Watch & discover

Part 1 of 19

Watch first

Planning a fair test

An English teaching video on this topic from Smart Learning Ltd. Watch it, then scroll down for the lesson.

Do it for real

The practicals below use what the film shows, with a full method you can follow at home.

The paper helicopter fair test Repeat readings and the anomaly hunt

In a nutshell

Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables

What you already know

Part 2 of 19

Before we start

What you already know

You should have carried out a simple practical and recorded results in a table.

Recap: Light: reflection, refraction and colour

Key words

Part 3 of 19

Key words

Words you'll need today

Independent variable: The one thing you deliberately change.
Dependent variable: The thing you measure.
Control variable: Something you keep the same so the test is fair.
Prediction: A statement of what you expect, with a scientific reason.
Repeatable: Gives similar results when the same person repeats it the same way.

Learning cycle

Part 4 of 19

Learning cycle 1 of 2

Choosing your variables

A short piece of teaching, then a check to make sure it has landed.

Explore the idea

Part 5 of 19

Learn

One change at a time

To test whether light intensity affects the rate of photosynthesis, the independent variable is distance from the lamp, the dependent variable is bubbles of oxygen per minute, and control variables include temperature, the same piece of pondweed, and carbon dioxide concentration. Change two things and you cannot say which caused the result.

Explore the idea

Part 6 of 19

Learn

Predictions with reasons

'Closer to the lamp gives more bubbles' is a guess. 'Closer to the lamp gives more bubbles because light intensity is higher, so more light energy is absorbed by chlorophyll and photosynthesis is faster' is a prediction. The reason is what makes it scientific and is usually worth the mark.

Quick check

Part 7 of 19

Quick check

In the pondweed investigation, the dependent variable is...

Quick check

Part 8 of 19

Quick check

Which is a control variable there?

Reset break

Part 9 of 19

Pause

That's sitting 1 of 2 done

Stretch, get a drink, look out of the window. There is no timer and nothing is counting down — your place is saved, so you can come back in five minutes or tomorrow.

Stop here for now

Learning cycle

Part 10 of 19

Learning cycle 2 of 2

Writing a method others can follow

A short piece of teaching, then a check to make sure it has landed.

Explore the idea

Part 11 of 19

Learn

A method someone else can repeat

Numbered steps, exact quantities, named equipment and measuring instruments, how many repeats, and how you will keep each control variable the same. A reader must be able to follow it without asking you a single question - that is the test of whether your method is good enough.

Explore the idea

Part 12 of 19

Learn

Range, interval and safety

Choose a sensible range, say 10 to 50 cm, with equal intervals of 10 cm, giving five results plus repeats. Too narrow a range hides the pattern; too few points make it unreliable. Add the real hazards and precautions - hot lamp, water near electricity - because a plan without them is incomplete.

Quick check

Part 13 of 19

Quick check

The best prediction is...

Quick check

Part 14 of 19

Quick check

A range of 10-50 cm at 10 cm intervals gives...

Common mix-ups

Part 15 of 19

Common mix-ups

Things people often get wrong

The independent variable is what you change; the dependent is what you measure.
'Keep everything the same' is not enough - name the control variables.
A prediction without a reason is only a guess.
Repeats improve reliability; they do not fix an unfair test.

Challenge round

Part 16 of 19

Game · Sort it

Which of these are true?

Drag each card into the right column. Tap a card first if dragging is fiddly.

True

Not true

Challenge round

Part 17 of 19

Game · Fill the gaps

Finish the sentences

Choose the word that belongs in each gap.

The reason is what makes it ____ and is usually worth the mark.

Mastery quiz

Part 18 of 19

Marked quiz

End of lesson quiz: Planning a fair test

6 questions, marked with the reasoning shown. No timer.

1. The independent variable is...
2. Repeats are done to...
3. A method is good enough when...
4. Too narrow a range risks...
5. Control variables exist to make the test...
6. A plan without hazards and precautions is...

Lesson round-up

Part 19 of 19

Lesson round-up

Ready when you are

Quiz score

Not sat

Games

Not played

Points this lesson

Best run

0 in a row

Luna: 0 out of 4 on the practice checks. Only if you feel up to it — one more?

Ask Luna

Do the work

Your written work for this lesson

This is the part you'd do in your book at school. Pick the pieces below, write here or on paper, and photograph anything you draw or work out.

Case study

Why the school greenhouse failed

A science club grew tomato plants in the school greenhouse. In June the plants grew well: leaves were dark green and the fruit set quickly. In July the club went away for two weeks and left the greenhouse door shut. When they came back, the leaves were curled and pale and most of the fruit had dropped.

The club had a data logger inside. It showed the temperature reached 46 °C on several afternoons and the soil moisture fell close to zero. The club knew photosynthesis needs light, water and carbon dioxide, and that enzymes in a plant work best in a narrow range of temperature. Above that range the enzymes stop working properly.

The club repeated the summer with the door propped open and a water bottle drip on each pot. Temperature peaked at 31 °C and the plants survived.

Written for Good Learning Co.

Reading questions

Name the variable the club changed the second time, and one variable they kept the same.
Explain, using the words photosynthesis and enzymes, why the plants were damaged in July.
Write a conclusion for the club's report, saying how far the evidence supports it.

Method and results
Writing
Write the aim, what you changed, what you measured and what you kept the same, then record your results in a table.
1 page + results table
Conclusion
Writing
Explain what your results show and why, using the scientific words from the lesson. Say how you know you can trust them.
6–8 sentences
Labelled diagram
Diagram
Draw the apparatus or the process in pencil, label it fully, and photograph it.
1 labelled diagram
Reading and notes
Reading
Read the lesson text again and write the key ideas in your own words.
Half a page of notes

Write your answer, notes or working here

Saved as you type.

Photos of paper work, diagrams or working outHow many minutes did the written work take?

Part 1 of 19 · Watch & discover

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Select, plan and carry out the most appropriate types of scientific enquiry to test predictions, including identifying independent, dependent and control variables