GCSE Maths is more than just numbers and equations — it’s about problem-solving, logical thinking, and applying mathematical skills to real-life situations. It’s also one of the most important qualifications you’ll take, influencing your options for A-levels, apprenticeships, and even certain job opportunities.
But here’s the truth: many students lose marks not because they don’t understand the maths, but because they make avoidable mistakes. These mistakes can range from rushing through questions, forgetting to include units, or making simple calculator errors.
At Read With Us, we help students strengthen their maths skills, practise exam techniques, and learn how to avoid the most common errors in GCSE Maths. This guide will walk you through 12 common mistakes students make, with detailed examples, correction tips, and revision strategies — so you can secure every possible mark.
Under exam pressure, students often skim-read questions and rush into calculations without noticing key details. GCSE examiners know this — which is why they deliberately include specific conditions like rounding instructions, units, or certain variables that must be found.
Calculating perimeter instead of area.
Answering in metres when the question asks for centimetres.
Solving for x when the question asks for y.
Ignoring a phrase like "to 1 decimal place" or "estimate".
Question: A garden is a rectangle measuring 12 metres by 8 metres. Find the perimeter.
Common mistake: Student calculates the area:
12 × 8 = 96 m² (incorrect).
Correct method:
Perimeter = 2 × (12 + 8) = 2 × 20 = 40 m (correct).
Tip: Underline perimeter in the question before starting.
Visual description: Diagram of a rectangle with dimensions labelled, "Perimeter" highlighted in red.
Extra support: If you often misread questions, our tutors at Read With Us can teach you active reading strategies for maths exams.
Some students skip working out to save time or because they think the answer is obvious. But in GCSE Maths, method marks mean that you can still earn points even if the final answer is wrong.
Examiners award marks for your method, not just your answer.
It shows your thought process.
A small calculation slip won’t cost you everything if your working is correct.
Question: Solve 2x + 5 = 15
No working shown: Writes x = 5 (wrong due to a calculation slip).
With working shown:
2x + 5 = 15
2x = 15 - 5
2x = 10
x = 10 ÷ 2 = 5 (correct).
Visual description: Step-by-step algebra solution in column format.
Tutoring tip: In our one-to-one maths tutoring sessions, we train students to write clear, examiner-friendly working every time.
Many students don’t fully understand their calculator’s functions — especially for fractions, powers, and brackets — leading to wrong answers.
Forgetting brackets.
Misreading scientific notation.
Rounding too early.
Question: Calculate (5 + 3²) ÷ 2
Wrong without brackets: 5 + 3² ÷ 2 = 5 + 4.5 = 9.5 (incorrect).
Correct: (5 + 9) ÷ 2 = 14 ÷ 2 = 7 (correct).
Visual description: Side-by-side calculator screenshots showing incorrect vs correct bracket use.
Marks are lost when students give a number without the correct unit.
Question: Perimeter of a square is 20 cm. Find one side.
Side = 20 ÷ 4 = 5 cm (unit must be included).
Visual description: Diagram of a square with all sides labelled.
Tip: Circle the units in the question before starting.
Spending too long on one tricky question means you might miss out on easier marks later.
How to Avoid It:
1 mark = 1 minute rule.
If stuck, move on and return later.
Use timed practice papers.
Extra help: At Read With Us, we give students timed drills to build speed and accuracy.
Missing negative signs.
Incorrectly combining terms.
Skipping steps.
Simplify 3x + 4x - 2
= (3x + 4x) - 2
= 7x - 2
Extra resource: Download our free algebra sheet at Read With Us.
Rounding too early can lead to wrong answers.
Rule: Only round at the very end unless told otherwise.
Tip: Convert all probabilities to the same format and check totals = 1.
Tip: Use flashcards and revise weekly.
Leave 5–10 minutes to review answers.
If a simple method works, use it.
Past papers are essential — mark them with official mark schemes.
Keep an error log.
Practise under exam conditions.
Focus on weak topics.
Use Read With Us resources for structured revision.
GCSE Maths success depends as much on avoiding mistakes as it does on learning the content. By reading questions carefully, showing your working, managing your time, and practising regularly, you can improve accuracy and confidence.
At Read With Us, we help students master these skills through targeted tuition and exam-focused strategies.
Reduce exam stress with our supportive tutors – book your session today!
