Science // Scientific Inquiry

Controlling variables

Plan different types of scientific enquiries to answer questions, recognising and controlling variables where necessary

Ages
9 to 11
Type
Thinking skill
Builds on
5 topics
Leads to
2 topics
Standards
1 code

Quick check

Can the learner plan their own experiment from scratch — deciding what to test, what to measure, what to keep the same, and how many times to repeat it?

Ask this to see whether the topic is secure.

Topic // Mastery

What mastery looks like

What a learner can do once this topic is secure.
  • Independently plan an investigation identifying the independent, dependent, and controlled variables
  • Choose the appropriate type of enquiry for the question (fair test, observation over time, pattern seeking, research)
  • Explain why controlling variables is essential for valid results

Topic // Map

Where this fits

What to learn first and what this topic opens up, with the reason for each link. Required links come first.
  • RequiredMust come first
  • HelpfulHelps, but not essential

Before this

5 topics
  • Fair testingRequired

    Scientific Inquiry // Ages 7 to 9

    Must set up simple fair tests before independently planning enquiries with variable control

  • Fair testing (age 8+)Required

    Scientific Inquiry // Ages 8 to 11

    Must plan enquiries with variable control before running fair tests on prototypes

  • Planning a TaskHelpful

    Learning to Learn // Learning to Learn // Ages 6 to 7

    Planning a scientific enquiry is the domain-specific application of the universal task-planning habit

  • Using evidence to answer questionsHelpful

    Scientific Inquiry // Ages 7 to 9

    Pattern identification supports planning targeted enquiries

  • Choosing a StrategyHelpful

    Learning to Learn // Learning to Learn // Ages 9 to 10

    Choosing an enquiry approach and evaluating whether it worked is the science form of the universal strategy-evaluation habit

You are here

Controlling variables

Ages 9 to 11 // Thinking skill

Leads to

2 topics
  • Fair testing (age 9+)Required

    Scientific Inquiry // Ages 9 to 11

    Must plan enquiries independently before designing follow-up investigations from predictions

  • Controlling variables (age 11+)Required

    Scientific Inquiry // Ages 11 to 12

    KS3 hypothesis formation and full experimental design extends KS2 Upper ability to plan enquiries and control variables

Topic // Research-informed

Teaching notes

From the Marble Skill Taxonomy. These notes have not been validated in classrooms, so treat them as a starting point for your own judgement.

The approach

For ages 9–11: pupils learn to plan scientific enquiries by choosing the right enquiry type for a question and, within a fair test, assigning each factor as the variable to change (independent), measure (dependent), or keep the same (control), and justifying why control makes a result valid. The central active experience is designing a plan and seeing how an uncontrolled variable makes a result impossible to interpret. Supporting activities assess variable roles and enquiry-type matching and probe pupils' justifications. Alternatives include categorisation-and-matching questions and a Socratic plan-interrogation; a labelled reference image is a scaffold only.

Common misconceptions

  • Defaulting to a fair test for every question, including ones better answered by observing over time, pattern-seeking, classifying or research (the AKSIS over-default persists into upper KS2).
  • Listing controlled variables without understanding why control is necessary — not connecting uncontrolled variables to invalid, uninterpretable results.
  • Confusing the independent (changed) and dependent (measured) variables, or thinking the thing you measure is something you set.
  • Believing 'more variables changed = a better/bigger experiment', missing that changing more than one destroys attribution.
  • Thinking planning is a formality to rush past, rather than the step that determines whether the results can answer the question at all.

Useful representations

  • A five-enquiry-type selector (fair test / observe over time / pattern-seek / classify / research) matched to question types
  • An independent – dependent – control variable planner (the formalising of change/measure/keep-the-same)
  • A planning proforma from question through to recording method
  • A 'which variables must we control, and why?' annotated set-up
  • A decision flow: what kind of question is this → which enquiry answers it best

Teaching practices

  • Teach enquiry-TYPE selection explicitly against the five named types, using questions that are NOT best answered by a fair test (e.g. 'how does the moon's shape change over a month?' → observing over time; 'do taller children have longer arms?' → pattern-seeking) so pupils stop reflexively reaching for a fair test (the AKSIS over-default).
  • Move pupils from teacher-set to self-planned: give the question and have them decide the variables and the enquiry type, then justify their choices — planning independence is the assessed step-up from earlier fair-testing.
  • Require the 'why control?' justification for each controlled variable ('we keep the water amount the same because otherwise we couldn't tell if temperature or water amount caused the change') — controlling variables is understood, not just listed.
  • Introduce the input/output/kept-same language (independent/dependent/control in child-friendly form) as a bridge to the KS3 vocabulary, without over-formalising at this age.
  • Use a planning proforma (question → enquiry type → variable to change → to measure → to control → prediction → how to record) so the full plan is visible before any doing.

Activities to try

  1. 1

    Design the plan, then run it: make a confound wreck your experiment

    Why it works: Controlling variables is not a rote rule: it removes rival explanations so a difference in results can be attributed to the one thing you changed. Changing more than one factor does not make the experiment stronger — it makes the cause unknowable. Different questions need different enquiry types, so a fair test is not always the right tool.

    1. Take a real question (e.g. 'Do plants grow taller with more sunlight?') and plan an investigation before doing anything.
    2. Choose one enquiry type from the five: fair/comparative test, observing over time, pattern-seeking, classifying/identifying, or research.
    3. Sort each factor into 'change' (the one input you vary), 'measure' (the output/result), and 'keep the same' (controls).
    4. Run the plan. If you left factors uncontrolled — e.g. the sunny plant also got more water and a bigger pot — observe how the result comes back ambiguous: 'light, water and pot size all differed, so we can't say which caused the growth.'
    5. Fix the plan by keeping every other factor you can the same so only one is changed, re-run, and compare how a cleaner plan gives an answer you can more fairly put down to that one change.
  2. 2

    Sort the variables and match the enquiry type

    Why it works: Pupils can distinguish the thing you set from the thing you measure, and can pick an enquiry type fit to the question — the knowledge that underpins independent planning.

    1. Categorise a list of factors in a given investigation into independent (change), dependent (measure), and control (keep the same) roles.
    2. Match several questions to their best-fitting enquiry type among the five named types.
    3. Answer 'why must we keep X the same?' by naming the rival explanation it rules out.
  3. 3

    Interrogate the plan: what else might be affecting your result?

    Why it works: Articulating and defending a plan can surface hidden confounds and push the 'why control?' reasoning to become explicit.

    1. Present a draft investigation plan to a 'scientist' partner or mentor.
    2. Respond to probing questions such as 'What else might be affecting your result?' and 'Which rival explanation does each control rule out?'
    3. Revise the plan to remove hidden uncontrolled variables and to confirm the enquiry type fits the question.

Topic // Standards

Curriculum standards

Codes for the curriculum statements this topic maps to. Each publisher owns its standard text.
The national curriculum in England: Key stages 1 and 2 framework document
KS2U.Sci.WS.1

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