Two ways to modify the same Chemistry practical. First: "we repeated the rate of reaction experiment with more temperatures." Second: "the class practical measured the reaction of sodium thiosulfate with hydrochloric acid across a temperature range too narrow to separate two effects, so this modification holds temperature constant and varies thiosulfate concentration across six values." Both are feasible. Only the second is justified, and that one word is the gap between the middle and top bands of the criterion worth a quarter of the task.
The other thirty internal marks
Queensland science subjects carry 50 internal marks. Our companion guide to the research investigation, criterion by criterion covers 20 of them. This one covers the other 30: IA1 the data test, and IA2 the student experiment.
- IA1 Data test10 marks
- IA2 Student experiment20 marks
- IA3 Research investigation20 marks
- External examination50 marks
Seven subjects share exactly this shape under the 2025 syllabuses: Biology, Chemistry, Physics, Psychology, Agricultural Science, Marine Science, and Earth and Environmental Science. The instruments, the marks and the marking guides are identical in all seven, so the skill of writing to this rubric moves with you between them. Check your own subject on the QCAA subjects hub, and see how the four instruments combine on the subject result calculator.
IA1: the data test
The data test is the only internal instrument sat under exam conditions, and it is short.
The stimulus is unseen, but its source is not: the data comes from Unit 3 work you have already done. Reviewing what each Unit 3 practical measured and what its data looked like is direct preparation.
The paper is weighted by cognitive demand, not topic. Roughly 30% of the marks go to determining unknown scientific quantities or features of datasets, roughly 30% to identifying trends, patterns, relationships, limitations or uncertainty, and roughly 40% to drawing conclusions based on analysis of datasets.
That 40% is the part students under-prepare. The verbs QCAA lists for it are deduce, determine, draw a conclusion, extrapolate, infer, interpolate, justify and predict. None of those are recall verbs, and each has a defined meaning worth knowing before you sit the test — our guide to the QCAA cognitive verbs works through them.
There are also no criteria to balance: a single guide runs from 10 down to 0 against the proportion of the paper answered correctly, with the top mark above 90%. Nowhere to make up a lost mark.
IA2: four criteria, not the IA3 four
The student experiment asks you to modify — refine, extend or redirect — an experiment relevant to Unit 3 subject matter, to address your own related hypothesis or question. It is marked out of 20 across four criteria worth 5 marks each.
- Forming5 marks
- Finding5 marks
- Analysing5 marks
- Interpreting and Evaluating5 marks
Read those names next to IA3's and you will see the trap. The research investigation splits the same vocabulary as Forming and Finding, Analysing, Interpreting, Evaluating. Here, Forming and Finding are separate criteria and interpretation is bundled with evaluation. A plan built from an IA3 exemplar gives five marks of attention to the wrong things.
Forming: justified, not merely feasible
Forming covers the rationale, the modification, the research question, the methodology and your referencing. One pair of words in the band wording does most of the work.
-
4–5
considered and justified
A considered rationale for the experiment, justified modifications to the methodology, a specific and relevant research question, a methodology that enables the collection of sufficient and relevant data, and appropriate use of genre and referencing conventions.
-
2–3
reasonable and feasible
A reasonable rationale, feasible modifications to the methodology, a relevant research question, a methodology that enables the collection of relevant data, and use of basic genre and referencing conventions.
-
1
vague or inappropriate
A vague or irrelevant rationale, inappropriate modifications, and a methodology that causes the collection of insufficient and irrelevant data.
A modification that could be done is feasible. One you have argued for is justified. Most drafts describe what was changed and stop, which is a textbook 2–3. The top band needs the reason the change was worth making.
Feasible (caps at 2–3)
"The original practical used three concentrations. This experiment uses six concentrations and repeats each trial five times."
Justified (reaches 4–5)
"The original practical used three concentrations, too few to distinguish a linear relationship from a saturating one. This experiment uses six across the same range, five trials at each, so the shape of the curve can be resolved and the spread at each point estimated."
The second version says what was insufficient about the published method and what the change makes possible. That is the structure of a justification, and it works for any modification: the limitation, the change, the consequence.
Do not skip the last bullet either. Genre and referencing conventions are marked inside Forming, so a report that reads like a lab worksheet loses marks in the criterion students think is only about design.
Finding: the quietest five marks
Finding is a separate 5-mark criterion here, and the one most often forfeited by omission. Its top band needs three things: considered management of risks, ethical issues and environmental issues; collection of sufficient and relevant raw data; and fluent and concise use of scientific language and representations.
- The risk assessment appears in the report and its outcomes are accounted for in the methodology, not filed away as a separate form.
- Raw data is shown, not only processed data. Sufficient means enough trials and enough levels of the independent variable.
- Units, significant figures, symbols and table conventions are correct throughout.
"Considered" management means you worked out which risks apply to your modified method and what you changed because of them. Copying the original safety notes after adding a higher temperature or a new reagent is the gap this descriptor catches.
Analysing: uncertainty is half the criterion
Analysing wants correct and relevant processing of data, thorough identification of relevant trends, patterns or relationships, and thorough and appropriate identification of the uncertainty and limitations of evidence.
The band language moves from "obvious" to "relevant" and from "basic" to "thorough". Identifying that the graph goes up is obvious. Identifying the relationship, quantifying it, and saying where it holds and where it breaks down is thorough.
Uncertainty and limitations both sit here rather than in the evaluation, and they are different things. Uncertainty is the numerical spread in your measurements: instrument resolution, the range across repeats, error bars. A limitation is a feature of the method that restricts what the evidence can support. Three sentences about human error covers neither.
The mean rate increased with concentration across all six levels. The relationship is linear between 0.05 and 0.20 mol L⁻¹ and flattens above it, and the spread across five trials at the highest concentration was more than twice that at the lowest, so the evidence supports the linear region more strongly than the plateau.
Why this scores: it names the relationship, bounds where it holds, quantifies uncertainty from the actual repeats, and says what that does to the evidence — trend and uncertainty in one move.
Interpreting and Evaluating: three jobs, five marks
The last criterion fuses two things IA3 keeps apart, and it has three top-band requirements: justified conclusions linked to the research question, a justified discussion of the reliability and validity of the experimental process, and suggested improvements and extensions that are logically derived from the analysis of evidence.
Reliability and validity are not synonyms. Reliability is consistency: would repeating the method give you the same data? Validity is whether the method measured what the research question asked about, including whether your controlled variables really stayed controlled. Justify each claim from your own results, not from general statements about experimental science.
"Logically derived from the analysis of evidence" is the constraint on the last bullet. An improvement earns marks when it fixes a limitation you identified in Analysing. An extension is the next question your data raises. Generic suggestions — more trials, better equipment — are related to nothing in particular, which is the middle band by definition.
The conditions, and what may be shared
That allowance is narrower than it looks. Everything on the list is data collection; nothing is writing. The rationale, the justification, the analysis and the evaluation are individual work, and every mark in the ISMG is awarded on those. Shared results with individually written analysis is correct; a shared draft is not. The academic integrity rules set out where that line sits.
Key takeaways
The student experiment rewards argument about method, not effort spent on method.
- Justify the modification. The limitation, the change, what the change makes possible. Feasible caps you at 2–3.
- Do not lose Finding by omission. Risk management, raw data and clean scientific language are a full quarter of the task.
- Separate uncertainty from limitations. Both live in Analysing, and both must be specific to your data.
- Read the "and/or". Reliability and validity. Improvements and extensions. The top band needs both halves.
- Prepare the data test from Unit 3. The stimulus is unseen but its source is not, and 40% of it is conclusions.
Check your experiment with ISMGenius
ISMGenius reads your draft against your task's own ISMG and shows you, criterion by criterion, which band your rationale, modification, analysis and evaluation reach, with the descriptor wording behind each. For this task that means learning whether your modification reads as justified or merely feasible while you can still fix it. It is an informed estimate to guide revision, not your official grade, and it never writes the work for you.
You can run a draft through ISMGenius, read the companion guide to the research investigation, learn how to read your ISMG before you write, and check how an ISMG rubric is structured. The syllabuses and marking guides themselves are published on the QCAA science subject pages.
