One of the most consistent findings across recent Chemistry Examiner’s Reports is that experimental design and data interpretation questions quietly separate score bands. These questions are rarely the longest on the paper, and they often look approachable. Yet year after year, they produce some of the widest spreads in student performance.
The reason is simple. Experimental design questions test whether students understand Chemistry as a scientific process, not just as a body of content.
How experimental design is assessed in the Chemistry exam
The Chemistry examination specifications make it explicit that key science skills are assessed across the entire paper. This includes identifying variables, analysing data, evaluating reliability and validity, and justifying conclusions using evidence. These skills are not confined to one section. They appear in multiple-choice questions, short-answer responses, and extended-answer tasks.
In the 2024 examination, experimental design skills were assessed through:
- interpretation of graphical and tabulated data
- identification of independent and dependent variables
- evaluation of limitations in experimental procedures
- explanation of how design choices affect reliability and accuracy
Importantly, students were rarely asked to design a full experiment from scratch. Instead, they were asked to interrogate an existing investigation and make judgements about it. This is a far more demanding skill.
Why students struggle with variables
One of the most common errors identified in the 2024 Examiner’s Report was incorrect identification of variables. Students frequently named quantities mentioned in the question stem without considering their role in the investigation.
For example, students often confuse controlled variables with conditions, or they identify an outcome rather than the dependent variable being measured. This suggests surface reading rather than analytical reading.
High-scoring responses clearly distinguish:
- the independent variable as the factor deliberately changed
- the dependent variable as the measurable outcome
- controlled variables as factors held constant to ensure a fair test
These students anchor their answers in the purpose of the experiment, not the wording of the question.
Data interpretation versus data description
Another consistent issue is the difference between describing data and interpreting it.
The Examiner’s Reports repeatedly note that many students simply restate trends visible in a graph or table without explaining what those trends show in chemical terms. For example, students might say that a graph “increases then plateaus” without linking this pattern to equilibrium, reaction completion, or limiting reagents.
High-scoring students interpret the data. They explain why the pattern occurs and what it indicates about the chemical system. This distinction is critical. Description earns limited marks. Interpretation earns full marks.
Evaluating reliability and validity properly
Questions that ask students to comment on reliability or validity are among the most poorly answered in Chemistry exams.
In the 2024 examination, many students responded with generic phrases such as “human error” or “equipment error”. The Examiner’s Report makes it clear that such responses lack specificity and are not rewarded.
Strong responses identify:
- a specific source of uncertainty
- how that uncertainty affects the data
- whether it impacts reliability, accuracy, or validity
For example, referring to inconsistent temperature control and explaining how it affects reaction rate demonstrates understanding. Simply stating that “temperature could change” does not.
Suggestions for improvement must address the limitation
Another frequent issue occurs when students are asked to suggest improvements to an experiment.
The Examiner’s Reports note that students often suggest improvements that are unrelated to the stated limitation. For instance, recommending “repeat the experiment more times” when the issue is systematic error does not demonstrate understanding.
High-scoring responses propose changes that directly address the identified weakness. This shows that the student understands both the problem and the solution, rather than relying on memorised laboratory advice.
Why these questions matter so much
Experimental design questions are powerful discriminators because they cannot be answered through memorisation alone. They require students to think like scientists.
Students who understand the chemistry content but do not understand how that content is generated, tested, and evaluated often lose marks here. Students who understand the logic of experimentation perform strongly, even when the context is unfamiliar.
This is why these questions appear consistently across years. They assess genuine scientific literacy.
An ATAR STAR perspective
At ATAR STAR, we see that students often improve rapidly in Chemistry once experimental design stops feeling abstract. When students learn to read experiments with intent and to justify their reasoning precisely, their confidence and accuracy increase across the entire paper.
This benefits students aiming for the highest scores, because it eliminates easy-to-lose marks, and it supports developing students by giving them a clear framework for approaching unfamiliar questions.