Every IGCSE Science examiner report says the same thing: most marks are lost to a small set of recurring mistakes, not to gaps in content. Students who have revised the syllabus carefully still drop marks they could keep — by misreading command words, omitting units, confusing similar terms, or describing where the question asked for an explanation. With Cambridge IGCSE Sciences running through May and Pearson Edexcel International GCSE sittings in the same window, this is the moment to make sure those mistakes are not the ones that decide your grade.

The twelve mistakes below are drawn from published examiner reports for Cambridge IGCSE Biology (0610), Chemistry (0620) and Physics (0625) and Pearson Edexcel International GCSE Biology (4BI1), Chemistry (4CH1) and Physics (4PH1) in recent series. Each comes with the mark-scheme penalty, the correction, and a drill you can use this week.

How examiner reports actually work

Each board publishes an examiner report after every series, summarising what cohorts did well, what they did badly, and where marks were typically lost. The reports are public. They are also the most under-used revision document for IGCSE Sciences. If you have not read the examiner report for last year’s paper in the subject you are sitting, do that this week — it is more useful than any third-party revision guide.

The mistakes below are the ones that examiner reports flag every year, across boards and across subjects. They are the slow-moving patterns of the IGCSE Science cohort, not single-paper anomalies.

The 12 most common mistakes

1. Confusing “describe” and “explain”

The single most common mistake across all three sciences. “Describe the trend shown in the graph” asks for direction, magnitude and any change in pattern — not the cause. “Explain why the rate of reaction increases as temperature rises” asks for a causal mechanism — not a description.

• Penalty: A correctly described trend on an “explain” question typically scores half marks at most. A correctly explained mechanism on a “describe” question scores zero on that marking point.
• Correction: Circle the command word before you read the rest of the question. Match your verbs to the question’s verb. See Cambridge, Edexcel, AQA & IB command words compared for the full breakdown.
• Drill: Take five past-paper questions where the command word is “explain”. Write the first sentence of each answer. Check that every sentence contains “because” or “therefore”. If it does not, rewrite.

2. Missing units in calculation answers

In Physics and Chemistry, answers without units lose marks even when the number is correct. Cambridge and Edexcel mark schemes typically allocate one mark for the calculation method, one for the value, and one for the unit. A correct number with no unit forfeits the unit mark.

• Penalty: Typically 1 mark per missing unit on a 3-mark calculation. Across a 90-mark Physics paper, this can be 5–8 marks for a student who is consistently inconsistent with units.
• Correction: Include units in every line of working, not just the final answer. Box the final answer with its unit. Pair this drill with the 2026 formula sheets hub so the formulae and their expected units sit on the same page.
• Drill: Mark your last past-paper script for unit omissions only. Count them. The number is usually higher than students expect.

3. Imprecise IGCSE Biology definitions

Cambridge IGCSE Biology mark schemes are unusually strict on definitions. “Osmosis is the movement of water across a membrane” misses the marks for net movement, water molecules, partially permeable membrane and the water potential gradient. The full mark-scheme definition awards marks for each underlined element separately.

• Penalty: A loose definition typically scores 1 of 3 or 1 of 4 marks. Across the paper, this is the largest source of mark loss in Biology after command-word errors.
• Correction: Use the syllabus wording for definitions. Not a paraphrase. The wording is in the official syllabus document and in the mark scheme. The Tutopiya definition-keyword lists publish board-aligned 2026 definitions for IGCSE Biology, Chemistry and Physics so you can drill from the same wording the marker has in front of them.
• Drill: Build a flashcard for every definition in the syllabus glossary, with the exact mark-scheme phrasing on the answer side. Drill them twice a day in the final fortnight using the flashcard maker.

4. Mole calculations: skipped or wrong stoichiometry

In IGCSE Chemistry, the most common Chemistry mark loss is in mole calculations — typically because students treat the molar ratio as 1:1 when the balanced equation says otherwise.

• Penalty: A wrong molar ratio cascades through the whole calculation. A 4-mark mole question often becomes a 1-mark question (for the formula mass) when the ratio is missed.
• Correction: Write the balanced equation first. Identify the molar ratio explicitly. Then proceed with moles → mass / volume / concentration. Keep the Chemistry formula sheet alongside as a reference for mole, yield and atom-economy relationships you must memorise (most boards do not print these in the exam).
• Drill: Take a stoichiometry past-paper question. Solve it three times: once at full speed, once writing every step out, once writing the balanced equation in red ink before any other working. The third method is the one that scores marks.

5. Physics: confusing speed, velocity and acceleration

In Physics calculation and definition questions, candidates frequently use speed when velocity is required, or velocity when acceleration is required. Each is a distinct concept with a distinct unit and a distinct equation.

• Penalty: Definition marks lost for using the wrong term; calculation marks lost when the wrong equation is selected.
• Correction: Memorise the three definitions and their units exactly: speed (m/s, scalar), velocity (m/s, vector), acceleration (m/s², vector). On every calculation, identify which is being asked for before you write an equation.
• Drill: Flashcards for all three definitions, plus 10 past-paper calculation questions where the candidate has to identify the correct quantity before solving.

6. Drawing a graph without labelling axes or units

Across Biology, Chemistry and Physics, graph questions lose marks for axes without units, missing scales, plotted points outside the line of best fit, or a line drawn through every point rather than as a smooth best-fit curve.

• Penalty: A 4-mark graph question typically allocates 1 mark for axes, 1 for scale, 1 for plotting, 1 for the line. Missing any element loses the corresponding mark.
• Correction: Use the mark-scheme checklist for graphs: axes labelled with quantity and unit, sensible scale, points plotted to ±half a small square, a smooth line of best fit (not “join the dots”).
• Drill: Practise three graphs from past papers. Self-mark against the mark scheme. Identify which element you missed each time.

7. Practical / Alternative-to-Practical: confusing “result” and “conclusion”

In Cambridge IGCSE Science Paper 6 (Alternative to Practical), candidates often write the conclusion in the “results” section, or vice versa. The mark scheme penalises both.

• Penalty: Marks are split between observations, results table, calculations and conclusion. Mixing them costs marks even when the science is correct.
• Correction: Read the question structure carefully. “Record your observations” and “State your conclusion” are different sections. Keep them separate.
• Drill: Take one past Paper 6 and split your answer into the explicit sections the mark scheme uses. Compare against the mark scheme line by line.

8. Ignoring “by reference to” or “using your data”

Many higher-tier IGCSE Science questions begin: “Using your data, explain…” or “With reference to the graph, suggest…”. Candidates often ignore the data and answer from general knowledge. The mark scheme is explicit: the marks are for using the named data, not for generic answers.

• Penalty: Generic answers without reference to the named data score zero on those marking points, even if the science is correct.
• Correction: Quote the data in your answer. “Between 25°C and 35°C, the rate doubled, which suggests…” not “As temperature rises, the rate increases…”.
• Drill: Mark your last data-response question for “data reference” — does every paragraph quote a specific value or trend from the named source?

9. Using everyday language for technical concepts

“The cell breaks down food to make energy.” The mark scheme wants respiration, glucose, oxygen (where appropriate), carbon dioxide, water, energy released for cellular processes. Everyday language scores below the technical vocabulary that the mark scheme rewards.

• Penalty: Top-band marks require technical vocabulary. Conversational answers score in the middle band.
• Correction: Build a list of the technical terms for each topic from the syllabus. Drill them as flashcards. Use them deliberately.
• Drill: Take an answer you wrote last week. Underline every word that is on the syllabus vocabulary list. If fewer than half the key words are present, rewrite.

10. Not showing working in show-that and prove-that questions

In Physics and Chemistry, “Show that the resistance is approximately 4Ω” awards marks for the method, not for the answer (which is given). Students who write only the final answer score zero.

• Penalty: A 3-mark “show that” with no working scores 0. With full working but a different final answer, partial credit is possible.
• Correction: Write every step. Substitute numbers. State the equation. Even when the answer is given, the marks are for the route to it.
• Drill: Find every “show that” question in two recent past papers. Solve each with explicit working. Compare to the mark scheme.

11. Misusing significant figures and decimal places

Mark schemes typically specify the number of significant figures expected. Answering 3.14159 when the question gave data to 3 significant figures is wrong — the answer should be 3.14.

• Penalty: Typically 1 mark per question on calculation papers. Across a Physics paper, this can be 3–5 marks lost.
• Correction: Match the significant figures of your answer to the least precise data in the question. If the question gives 3 sig figs, answer to 3 sig figs.
• Drill: Mark your last calculation paper for significant-figure errors only. Note the pattern.

12. Running out of time on the long-answer question

Long-answer (6+ mark) questions sit at the back of the paper. Candidates who pace badly arrive at them with 8 minutes left for a question that needs 12. Half-finished answers leave 4–6 marks on the table.

• Penalty: A half-finished 8-mark question typically scores 3–4 marks. A fully developed answer scores 6–8.
• Correction: Time-check at the halfway point of the paper. If you are behind, prioritise the long-answer question — it carries the most marks per minute available.
• Drill: Sit a full past paper under timed conditions. Note the time remaining at each question break. Plan a pacing target for the next paper.

Subject-specific common mistakes by board

The 12 mistakes above span all three sciences. Each board also has its own subject-specific patterns. Tutopiya publishes detailed lists for the major boards:

• AQA GCSE: see the AQA-specific lists for Biology, Chemistry and Physics.
• Cambridge International A-Level: see the Cambridge-specific lists for Biology, Chemistry and Physics.

For the full set of subject-specific common-mistakes lists across boards and qualifications, the Tutopiya Common Mistakes Lists tool is the single index.

A free tool that turns common mistakes into a revision plan

The Tutopiya Common Mistakes Lists tool aggregates examiner-report findings for Cambridge IGCSE, Pearson Edexcel International GCSE, AQA GCSE, Cambridge International A-Level and IB DP subjects into searchable, board-specific lists. You can:

• Filter by board, subject and topic to find the mistakes most likely to cost you marks on your next paper.
• Export to CSV or PDF for printing or sharing with a study group.
• Build a personal “watch list” of your most-frequent mistakes from your own past-paper marking.

It is free, browser-based, and aligned to the 2026 syllabus for each board. The lists are most useful when paired with the flashcard maker — turn each common mistake into a flashcard with the correct phrasing on the answer side, and drill them in the final fortnight.

How to use this list in the final fortnight

A practical pattern for the last 14 days before an IGCSE Science paper:

• Day 14–11: Read the examiner report for last year’s paper in your subject. Highlight every “common error” the report names. Add any not on the list above.
• Day 10–7: Mark your most recent past paper specifically for the 12 mistakes above. Score yourself on how often each one cost a mark. Build a personal top three.
• Day 6–4: Drill the personal top three with targeted past-paper questions — five questions per mistake. Self-mark against the mark scheme.
• Day 3–2: Final past paper under timed conditions. Mark for the same 12 mistakes. Compare to your day-10 baseline.
• Day 1: Light review of definitions and units. Sleep early.

Pair the mistake list with a subject revision checklist rated using the confidence-rating method, so the mistakes you correct on Red topics translate directly into your weekly plan. For the wider revision pattern that pairs common-mistake correction with active recall and timed practice, see active recall vs highlighting: why flashcards win the last two weeks and how to use past papers effectively for IGCSE 2026.

Frequently asked questions

What is the most common mistake in IGCSE Science exams?

Across Biology, Chemistry and Physics, the single most common mistake is confusing “describe” and “explain” — answering with a description when the question asks for a causal mechanism. The penalty is typically half marks or less on the affected question.

How do I avoid losing marks on IGCSE Science definitions?

Use the syllabus wording for definitions, not a paraphrase. Cambridge and Edexcel mark schemes award marks for specific phrases (e.g. partially permeable membrane, net movement of water molecules). A close-but-not-exact definition typically scores 1 of 3 or 1 of 4 marks.

Are units always required in IGCSE Physics and Chemistry answers?

Yes — calculation mark schemes typically allocate one mark for the unit, separate from the calculation and the value. A correct number with no unit forfeits that mark. Across a 90-mark Physics paper, this can be 5–8 marks for a student who is inconsistent with units.

How do examiner reports help with revision?

Examiner reports are published after every series and summarise what the cohort did well, what they did badly, and where marks were lost. The “common errors” sections are the most under-used revision document for IGCSE Sciences. Read the report for last year’s paper in your subject before your next past-paper drill.

What is the best way to drill common-mistake corrections?

Take a recent past paper and mark it specifically for the 12 mistakes above. Identify your personal top three. Drill those three with targeted past-paper questions — five questions per mistake — and self-mark against the mark scheme. Repeat with a fresh past paper at the end of the week.

How do I read a graph question correctly?

For “describe” the trend: state direction, magnitude and any change in pattern, with values from the graph. For “explain” the trend: state the cause and the mechanism. For “draw” a graph: axes labelled with quantity and unit, sensible scale, points plotted accurately, smooth line of best fit (not “join the dots”).

Why do I lose marks on “show that” questions even when my answer is correct?

“Show that” questions award marks for the method, not the answer (which is given). Writing only the final answer scores zero. Show every step: equation, substitution, calculation, final value with unit.

How do significant figures work in IGCSE Sciences?

Match the significant figures of your answer to the least precise data in the question. If the question gives data to 3 significant figures, answer to 3 significant figures. Mark schemes typically specify the expected precision; some accept a small range, others do not.

Where can I find common-mistake lists for my specific subject and board?

The Tutopiya Common Mistakes Lists tool aggregates lists by board, subject and topic for Cambridge IGCSE, Pearson Edexcel International GCSE, AQA GCSE, Cambridge International A-Level and IB DP. Subject-specific lists for AQA GCSE Sciences and Cambridge International A-Level Sciences are linked above.

Is the Tutopiya Common Mistakes tool free?

Yes — the Common Mistakes Lists tool is free, browser-based, and aligned to the 2026 syllabus for the major boards. There is no signup required to filter and download lists.

Can I use these mistake lists for my own teaching?

Yes — international school teachers and tutors use the lists as a mark-scheme calibration document for end-of-unit assessments. The CSV export is designed for use as a marking checklist or as a department resource.

How do these mistakes apply to IGCSE alternatives like O-Level or other boards?

The 12 patterns above (command-word confusion, missing units, loose definitions, weak data reference) are board-agnostic and apply to most international exam systems including Cambridge O-Level, Edexcel International GCSE and IB DP MYP. The specific subject content differs; the mistake patterns are the same.

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Last reviewed: 4 May 2026. Always cross-check definitions, mark-scheme expectations and unit requirements against your official 2026 syllabus and the most recent published examiner reports for your board and subject.

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