We have all seen it. A student gets the right answer but gets 0 marks.
Why? Because they missed a step in the working (M1) or the exam mark scheme specified "Correct Answer Only" (CAO).
Most students spend 100% of their revision time on content (formulae, definitions, dates). They spend 0% of their time revising how marks are awarded. This is often the difference between a Grade 7 and a Grade 9.
The Mark Scheme Cheat Sheet
We have updated
our guide to include more examiner codes and the specific traps that cause even the smartest students to lose marks.
If you are wondering what does A1 mean in math or what "ISW" stands for, here is the definitive guide. If you see these codes on a mark scheme, here is what they actually mean for your grade:
CAO (Correct Answer Only)
What does CAO mean in maths? It means you must have the
exact answer matching the mark scheme. No marks for "close enough," rounding errors, or correct methods if the final number is wrong.
ISW (Ignore Subsequent Working)
If a student gets the answer right but then adds a mistake afterwards (e.g., trying to simplify a fraction that didn't need simplifying and getting it wrong), the examiner ignores the extra mistake. The mark stands.
WWW (Without Wrong Working)
This is the danger zone. The answer is correct, but the logic used to get there was mathematically illegal. Zero marks awarded. The examiner checks the method, not just the final number.
SOI (Seen Or Implied)
The student didn't write the working, but their next step proves they must have done it correctly in their head. The mark is awarded.
OE (Or Equivalent)
0.5 is the same as 1/2. If the answer is mathematically identical to the
answer scheme, it counts.
AWRT (Answers Which Round To)
Accept any value within a specified range of accuracy (e.g., if the answer is 3.14159, "awrt 3.14" means 3.14 is accepted).
Bonus: What does B1 mean in maths mark scheme?
Unlike Method marks, a B1 mark is an independent accuracy mark. It is awarded for a specific correct statement or answer (like reading a graph correctly) independent of any method working.
Updated glossary for GCSE
Download our full
GCSE Maths Mark Scheme Cheat Sheet
here.
See it in Action: The £50,000 Rounding Error
Let's look at a typical
GCSE Maths question where a student loses a grade despite "knowing" the maths.
The Question:
Calculate the compound interest on £25,000 at 3.5% per year for 4 years. (3 marks)
The Mark Scheme:
- M1: For using 1.035 or equivalent multiplier
- M1: For £25000 x 1.035^4
- A1 (cao): £28,688.08
Student A (The "Premature Rounder")
- Calculation: "I'll do 1.035 x 1.035 x 1.035 x 1.035… oh, that's roughly 1.15."
- Answer: £25000 x 1.15 = £28,750
- Final Answer: £28,750
The Verdict:
- M1: Awarded (Used correct method)
- M1: Awarded (Set up the calculation)
- A0: ZERO. The answer is wrong because they rounded the multiplier too early.
- Result: 2 out of 3 marks.
Student B (The "CAO" Victim)
- Calculation: £28,688.0805... "I'll round it to the nearest pound."
- Final Answer: £28,688
The Verdict:
- M1: Awarded.
- M1: Awarded.
- A0: ZERO. The mark scheme specified CAO (Correct Answer Only).
- Result: 2 out of 3 marks.
Why this matters for your Department
Manually checking for "M" and "cao" errors across 200 mock papers is why teachers are exhausted. It is also why inconsistency creeps in at 11 PM on a Sunday, it is easy to miss a "Follow Through" mark or be too generous with rounding.
We built
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We trained our AI exam marking engine on thousands of real mark schemes to understand these nuances. It doesn't just check the final number; it traces the logic steps in student handwriting to award Method Marks (M1) and spot "Wrong Working" (WWW).
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