Why the Same Errors Appear Every Year
After every GCSE sitting, the chief examiner writes a report documenting how candidates performed on each question. These reports are public and freely available from AQA, Edexcel, and Cambridge. Read a few in sequence and a pattern emerges: the same mistakes appear with almost clockwork regularity. Not because students are unprepared, but because certain habits under exam pressure reliably produce the same errors. None of the ten mistakes below are intelligence failures. They are method failures — and every one of them can be corrected through deliberate practice.
The 10 Mistakes
These are drawn directly from patterns documented in AQA, Edexcel, and Cambridge IGCSE examiner reports over multiple years.
- 1. Not reading the question fully. The most expensive mistake of all. The word 'Hence' tells you to use a previous result — ignoring it and starting from scratch earns zero marks. 'Without a calculator' means showing full arithmetic. 'Give your answer in standard form' means the answer is wrong if it is not in standard form. Read every word before writing anything.
- 2. Rounding too early. Calculating an intermediate value, rounding it to 2 decimal places, and then using that rounded value in the next step compounds error. The examiner expects your final answer to be accurate to 3 significant figures — but your working values should stay unrounded until the last step. Use the memory function on your calculator to carry exact values forward.
- 3. Not showing method on 'show that' questions. 'Show that x² - 5x + 6 = 0' means the answer is given — the marks are entirely for working. A student who writes the target equation without derivation earns zero. Every step of the algebraic journey needs to be visible, logical, and clearly laid out.
- 4. Misreading graph scales. On a distance-time or velocity-time graph, each small square may represent 0.2 units, not 1. Students who assume every square is worth 1 unit misread coordinates, calculate wrong gradients, and give wrong areas. Count the squares between labelled values before reading any coordinate.
- 5. Forgetting units. A question about the area of a field expects m² or cm², not just a number. A speed question expects m/s or km/h. A money question expects £. Examiner reports flag this as a persistent issue across all ability levels. A correct numerical answer without units loses the accuracy mark on most questions.
- 6. Expanding brackets with sign errors. (x - 3)(x + 4) is not x² + 4x - 3x - 12 simplified — students frequently get the cross-term wrong when one or both brackets contain a negative. The safe habit: expand term-by-term, writing every product before simplifying. x times x = x², x times 4 = 4x, -3 times x = -3x, -3 times 4 = -12. Then collect.
- 7. Dividing instead of multiplying in proportion questions. If 5 items cost £12 and the question asks for the cost of 8 items, the proportion is 12 ÷ 5 × 8, not 12 ÷ 8 × 5. Under pressure, students invert the operation. The check: does your answer make sense? Eight items should cost more than five items.
- 8. Missing negative solutions in quadratics. x² = 9 has two solutions: x = 3 and x = -3. Students who write only x = 3 lose half the accuracy marks. The same applies to the quadratic formula — the ± symbol exists for a reason. Every time you take a square root in an equation, there are two solutions unless the context rules one out.
- 9. Confusing mean, median, and mode. In a grouped frequency table, the mode is the modal class, not the midpoint. The median requires cumulative frequency, not just dividing n by 2 and reading off. The mean from grouped data requires midpoints and fx. Mixing these up produces answers that are incorrect but plausible-looking, which is exactly when students do not double-check.
- 10. Not checking if the answer is reasonable. A triangle cannot have an interior angle of 200°. A person cannot be 15 metres tall. A probability cannot exceed 1. A speed of 0.003 km/h for a car is implausible. Taking five seconds to ask 'does this answer make sense?' catches errors that no amount of working can prevent.
The Pattern Examiners See Every Year
The common thread across these ten mistakes is that none of them are about not knowing the mathematics. A student who forgets units knows perfectly well that area is measured in square units — the habit just is not ingrained under pressure. A student who misreads graph scales has not forgotten how to read graphs — they have not made checking the scale automatic. The fix for every mistake on this list is the same: build the correct habit so automatically that exam pressure cannot override it. That means practising with mark scheme awareness, not just practising. After every past paper attempt, check not just whether your answers were right but which of these ten errors appeared. Tally them. The most common one is your priority.
A Systematic Checking Routine
With five minutes left at the end of a paper, a quick scan catches most of these mistakes.
- Did I read what each question actually asked? Check the command word and any constraints.
- Do my numerical answers have units where the question is about measurement, money, or rates?
- On any question involving a square root or factorisation, did I find both solutions?
- On graph questions, did I count the scale correctly before reading any values?
- Does each answer pass a rough sense-check — is the magnitude plausible?
Take the Diagnostic Quiz
Knowing which mistakes you personally make most often is more valuable than a general list. The free diagnostic quiz at MathsTutor.com identifies your specific weak topics with exam-style questions, so revision time targets the areas that will move your grade. Most students discover their top three issues within 15 minutes.