After working through hundreds of GCSE Maths papers, the same mistakes appear again and again. Not obscure errors on difficult topics, but recurring patterns that cost students marks across every paper, at every grade boundary. The frustrating thing is that most of them are entirely fixable with a small change in habit or approach.
This guide covers the mistakes we see most consistently, why they happen and exactly what to do differently. If you have mocks coming up, or if you are building towards the real exams, addressing these specifically will have a more direct impact on your grade than adding more hours of general revision.
This is the single most common and most costly mistake in GCSE Maths. Students who do working in their head or on a calculator and write only the final answer are handing back method marks every time they make a slip. GCSE Maths mark schemes award marks for correct method as well as correct answer. A student who sets up the right calculation but makes an arithmetic error partway through can still collect most of the available marks, provided the working is visible. A student who writes only the wrong answer collects nothing.
The fix is straightforward: write every step, every time, even when it feels unnecessary. This applies particularly to multi-step questions on algebra, geometry and problem-solving where the working is the evidence that you understood the method, regardless of whether the final answer is right.
The fixMake it a rule: if a question is worth two or more marks, there must be visible working. Write out each step clearly. If you get the wrong answer, you will still collect method marks. If you get the right answer, the working confirms it.
A student who knows how to find the area of a triangle but calculates the perimeter instead scores zero. A student who is asked for the probability of an event NOT occurring and gives the probability of it occurring scores zero. These are not knowledge gaps. They are reading errors, and they are responsible for a significant number of lost marks in every exam sitting.
GCSE Maths questions are carefully worded. Words like "show that", "hence", "estimate", "give your answer to 3 significant figures" and "not" are load-bearing. Missing or misreading any of them changes what a correct answer looks like.
The fixRead every question twice before writing anything. On the second read, underline or circle the specific thing being asked for. Check your final answer against what the question actually asked, not against what you thought it asked when you started working.
Multi-step calculations require you to carry full precision through intermediate steps and round only at the end. Students who round to two decimal places after the first step and then use that rounded value in the next calculation accumulate error. The final answer looks wrong, the mark scheme does not accept it and the student often cannot understand why.
This comes up particularly in trigonometry, Pythagoras, area calculations involving pi and any problem where you calculate an intermediate value and then use it again.
The fixKeep full calculator precision through every intermediate step. Only round your final answer, and only to the degree of precision the question specifies. If the question says "give your answer to 1 decimal place", that instruction applies to the final answer only.
An answer of 45 to a question asking for a length in centimetres scores no marks if the mark scheme requires "45 cm". An answer rounded to 2 decimal places when the question specifies 3 significant figures is wrong even if the underlying calculation is correct. These are single-mark losses that add up across a paper and are completely avoidable.
Rounding to significant figures rather than decimal places is a particular source of confusion. A common error is treating "3 significant figures" and "3 decimal places" as the same thing. They are not. 0.004521 to 3 significant figures is 0.00452. To 3 decimal places it is 0.005. Knowing the difference matters.
The fixAt the end of every answer, run a two-second check: does the question specify units? Does it specify how to round? If yes to either, make sure your written answer reflects that. One second of checking prevents one mark of loss.
GCSE Maths examiners deliberately present familiar topics in unfamiliar contexts. A question on ratio might be wrapped in a recipe problem. A question on algebra might be framed as a geometry puzzle. Students who only practise standard question formats freeze when the presentation changes, even though the underlying Maths is something they know.
This is one of the most significant gaps between students who score in the grade 5 to 6 range and those who push into 7 and above. The content knowledge is often similar. The ability to extract what is being asked and apply known methods to an unfamiliar wrapper is what separates the grades.
The fixWhen you encounter an unfamiliar question format, write down what you know before deciding you cannot do it. What information has the question given you? What topic area does it involve? What method applies to that topic? Starting this process almost always unlocks a route through, even on questions that initially feel impossible.
Algebra underpins a large portion of GCSE Maths. Errors in expanding brackets, collecting like terms, solving equations and rearranging formulae do not just cost marks on algebra questions. They create cascading errors across topics like simultaneous equations, quadratics, sequences and anything involving substitution. A student whose algebra is shaky loses marks in multiple places on every paper.
The most common specific errors are sign mistakes when expanding double brackets, incorrect operations when rearranging (dividing both sides rather than the whole expression), and losing negative signs when collecting terms.
The fixAlgebra needs consistent practice, not just recognition. Working through algebra questions without a calculator, checking each step, and specifically practising the operations you find unreliable builds the accuracy that prevents cascading errors later. If brackets and rearrangement are weak areas, address them directly rather than hoping they will sort themselves out.
GCSE Maths papers are timed to be challenging but completable. Students who run out of time almost always do so for one of two reasons: spending too long on questions they are stuck on early in the paper, or working slowly through easier questions without awareness of the clock. Either way, unattempted questions at the end of a paper are marks given away for free.
Each mark on a GCSE Maths paper is worth roughly the same amount of time. A 1-mark question deserves one minute. A 5-mark question deserves five minutes. Spending ten minutes on a 2-mark question you cannot do while leaving a 4-mark question unattempted at the end is a poor trade.
The fixPractise past papers under timed conditions, not just as exercises to work through at your own pace. If you are stuck on a question for more than two minutes, mark it, move on and return at the end if time allows. Attempting every question on the paper, even imperfectly, is almost always better than perfecting a few and leaving others blank.
Notice that very few of the mistakes above require learning new content to fix. They require changing how you approach papers: how you read questions, how you write working, how you manage time. This is good news. Habit changes can happen quickly. A student who addresses the seven points above before their next mock will score differently on that mock, not because they have revised more content but because they are using what they already know more effectively.
How to use this list before your next exam
Go through your most recent Maths paper, or your next practice paper, and mark which of these seven mistakes appear in your work. Most students find that two or three of them account for the majority of their lost marks. Those two or three are your specific targets for the period before mocks.
For each target mistake, identify the specific fix and practise it consciously on the next few papers you sit. A mistake you are aware of and actively correcting disappears within a few sessions. A mistake you are unaware of repeats indefinitely.
A note on Paper 1 specifically
Several of these mistakes are more costly on Paper 1, the non-calculator paper, than on Papers 2 and 3. Without a calculator, arithmetic slips are more likely, rounding errors from intermediate steps are harder to avoid without care and algebraic manipulation errors cannot be checked numerically. The habits of showing working and reading questions carefully matter on all three papers, but building them to be automatic before Paper 1 is particularly worthwhile.
Students who sit Paper 1 without having practised non-calculator arithmetic recently are also at a disadvantage. Mental and written arithmetic, fraction calculations, percentage changes without a calculator and exact trigonometric values all require fluency that degrades without practice. If Paper 1 is a weak point, dedicate some specific preparation time to it rather than treating all three papers as equivalent.
