MYP Physics: Controlling Variables — How Is It Assessed?

Controlling variables is assessed under MYP Sciences Criterion B: Inquiring and Designing, specifically strand ii, which asks you to describe how to control the significant variables and explain how this control will be achieved. Markers check your explanation is specific to your actual experiment, not generic.

A controlled variable is any factor besides your independent variable that could affect your results, so you deliberately hold it constant. In a pendulum investigation testing string length against period, controlled variables include the bob's mass, release angle, and where you start the stopwatch.

The independent variable is what you deliberately change; the dependent variable is what you measure as a result; controlled variables are everything else you keep fixed so the test is fair. Mixing these up is the single most common error I see in Year 4 lab reports.

Scientists control variables so any change in the dependent variable can be attributed only to the independent variable, making the test a fair one. Without control, you can't claim a cause-and-effect relationship — your data just shows correlation, and an examiner will mark that down as a validity issue.

Write each controlled variable as a specific value plus a method, not just a word. Instead of 'surface,' write 'the ramp surface will be kept as the same wooden board for every trial to avoid changes in friction.' Examiners reward this level of detail heavily in Criterion B.

The MYP Sciences guide uses 'describe' and 'explain' for this strand — describe the variables to be controlled, and explain how and why the control will be carried out. 'Explain' requires reasoning (why this matters), not just a list, which is where many students stop short.

There's no fixed number in the MYP: From Principles into Practice guide, but three to five genuinely relevant variables is realistic for most Year 4–5 investigations. Padding the list with trivial ones (like 'the colour of the desk') doesn't add marks and can make your reasoning look unfocused.

The top three mistakes: confusing a controlled variable with the independent variable, stating the variable without a fixed value, and giving no method of control at all. I mark dozens of reports where 'temperature' appears in the list with no number, no apparatus, and no explanation.

Controlling variables sits within Criterion B: Inquiring and Designing, strand ii — 'describe how to manipulate the variables, and describe how data will be collected.' It's assessed alongside your hypothesis and methodology, so a weak variables section pulls down the whole criterion, not just one line.

Yes — on-screen tasks in the MYP eAssessment for Sciences (available at the end of MYP 5) often include short-answer questions asking students to identify or justify controlled variables in a described experiment, separate from any classroom-based Criterion B task.

Criterion C: Processing and Evaluating asks you to discuss the validity of your method, and poorly controlled variables are the most common reason results turn out inconsistent. If you flagged a variable in Criterion B but it drifted during testing, that becomes a genuine limitation to evaluate in Criterion C.

MYP Physics assesses controlling variables through Criterion B command terms like 'describe' and 'explain,' scored out of 8. DP Physics folds the same skill into the Internal Assessment's exploration criterion, judged against broader 'methodology' descriptors rather than a dedicated variables strand — the underlying science is identical, but the marking language changes.

Yes — controlling variables falls under the same Criterion B strand across all MYP sciences, since the MYP Sciences guide is a single subject-group document covering Biology, Chemistry and Physics. The skill and mark scheme transfer directly between subjects, so practice in one science strengthens the others.

The fastest gains come from practising the specific write-up format examiners expect: a named variable, its fixed value, and the method used to control it, repeated for each factor. Reviewing past lab reports together and checking each variable against this three-part structure closes most of the gap within a term.