Mark Scheme Abbreviations Explained: CAO, ECF, OWTTE

Mark scheme abbreviations are shorthand that examiners use to say what earns a mark and what does not: CAO means “correct answer only”, ECF (or FT) means your earlier mistake is not punished twice, and M1, A1, B1 label method, accuracy and independent marks. Once you can read them, a mark scheme stops being a wall of code and becomes a list of instructions for exactly how to write your answer.

The set below covers GCSE and IGCSE papers from AQA, Edexcel and Cambridge. The core meanings are the same everywhere. Where a board does something differently, it is flagged. If you are new to the idea, start with what a mark scheme is, then come back to use this as a reference.

CAO, ECF and FT: marks for answers and for errors

• CAO — correct answer only. The mark is given for the right final answer and nothing else. Working is not credited for this mark. Example: “A1 cao” for 12.5 cm means 12.4 scores nothing here, even if your method was perfect (the method marks are separate).
• ECF — error carried forward. If you make a mistake early and then use your wrong value correctly in a later step, you can still earn the later marks. Example: you get the moles wrong in part (a), then use that wrong number correctly to find a mass in part (b); part (b) can still score in full.
• FT — follow through. Edexcel and AQA maths schemes usually write this one. It means the same as ECF: mark your working against your own earlier answer, not the examiner’s.

ECF and FT are why showing working matters so much. The examiner can only follow your wrong number through if they can see it.

OWTTE, ORA, OE and ISW: how strictly your wording is read

• OWTTE — or words to that effect. The mark scheme gives one wording, but any answer that means the same thing earns the mark. Example: “particles gain kinetic energy owtte” also accepts “particles move faster”.
• OE — or equivalent. Common in maths. A different but equivalent form is accepted. Example: 0.5 oe accepts ½ and 50%.
• ORA — or reverse argument. You can make the point from the other direction. Example: “higher temperature gives faster reaction ora” also accepts “lower temperature gives slower reaction”.
• ISW — ignore subsequent working. Once you have reached a correct answer, anything you do afterwards is not marked. Example: you write 3/6 then simplify wrongly to 1/3; if 3/6 earned the mark, the later slip does not cost you. Note that this protects a correct answer, not a wrong one.
• BOD — benefit of the doubt. The examiner is told to give the mark where the answer is unclear but probably shows the right idea. Do not rely on it. It is a rescue, not a strategy.

AWRT: answers within a range

AWRT means “anything which rounds to”, and Edexcel mark schemes use it a lot. Example: “awrt 3.14” accepts 3.1416 but not 3.2. Cambridge writes much the same idea as “art”. It exists so a correct value is not rejected for sensible rounding, which is also why you should keep extra digits in your calculator until the final line.

M1, A1, B1: the three kinds of mark

• M — method mark. For using a correct process, such as the right equation or substitution. Example: M1 for 0.5 × 1200 × 15². It can be earned even if the final answer is wrong.
• A — accuracy mark. For the correct result, but usually only if the matching method mark was earned. Example: A1 for 135,000 J.
• B — independent mark. A mark for a correct statement, value or step that does not depend on a method. Example: B1 for writing the unit correctly or for a correct value read from a graph.

The number is the count of marks, so M2 is two method marks. You will also see SC (special case), where the scheme gives partial credit for a common wrong approach, and dep (dependent), meaning a mark is only available if an earlier one was earned. Maths papers use this M/A/B system heavily. Science papers on AQA and Cambridge usually do not label marks this way and simply list the points that earn one mark each, so you will mostly meet the codes below instead. Full detail on this is in our guide to method marks.

AO1, AO2, AO3: assessment objectives

Assessment objectives describe what skill a question is testing. They are usually printed beside the marks or in a grid at the start of the scheme. Broadly, AO1 is recalling knowledge, AO2 is applying it to a situation, and AO3 is analysing or evaluating (in science, often handling data or experimental skills). The exact wording changes with the board and the subject, so check the front of your own mark scheme. For revision, the useful point is that AO1 questions reward accurate terms, while AO2 and AO3 questions reward using the information given in the question.

Allow, ignore, reject and do not accept

These tell you what the examiner must do with a particular phrase. They are some of the most useful lines in the whole scheme, because they show exactly where a near-miss falls.

• Allow — this alternative earns the mark. Example: “allow thermal energy” when the main answer is “heat”.
• Ignore — the examiner takes no notice of this phrase, so it neither earns nor loses a mark. Example: “ignore references to the particles being hot”.
• Reject — Cambridge wording. If you write this, you lose the mark, even if the correct answer is also in your response.
• Do not accept — the AQA equivalent of reject. Example: “do not accept the particles expand” when the correct idea is that they move further apart.

The difference between ignore and reject is the one students miss. An ignored phrase is harmless. A rejected phrase contradicts the right answer, so you can lose a mark by adding it. This is the main reason to stop writing everything you can think of and give one clear point per mark.

Underlined words, brackets, slashes and max

• Underlined words must appear, or an equivalent must be clearly given. Example: in “complementary shape”, the underlined term is the part that earns the mark. The scheme is telling you that the exact scientific word is required.
• Brackets ( ) usually mark something that is not needed to earn the mark but is acceptable. Example: “(carbon) dioxide” accepts either form.
• A slash / separates alternative answers, and any one of them earns the mark. Example: “diffusion / random movement” means either answer is fine, not both.
• Max caps the marks available for a group of points. Example: “max 2” beside a list of five acceptable points means that however many you give, only two marks can come from that group.

Cambridge science schemes also use a semicolon to separate individual marking points, so each semicolon is roughly one mark. Edexcel and AQA lay out the same ideas in a column, one point per row.

How to use all of this in revision

Read the mark scheme for a question you got wrong and translate each code. Was the lost mark an A1 you could have kept by checking your arithmetic, a rejected phrase you added by mistake, or a missing underlined word? Each one has a different fix, and none of them is “revise the whole topic again”.

Practise with the real wording of the board you sit. Use the worksheets for GCSE AQA Physics or work through Cambridge IGCSE Chemistry and see where each mark came from. For maths, the GCSE AQA Maths and Edexcel IGCSE Maths courses are where method, accuracy and follow-through marks matter most.

Practise with a marker that reads like an examiner

Knowing the codes is one thing; seeing them applied to your own answers is another. Every written answer you submit on Exaim is marked against the board’s own mark scheme, point by point, so you can see which mark you earned, which you lost, and why.