How Cambridge Mark Schemes Work: M1, A1 and B1 Explained

A Cambridge mark scheme is a table of marking points, not a model answer. Each row says what an examiner may credit, and codes such as M1, A1 and B1 say what kind of credit it is: M for method, A for accuracy that depends on that method, and B for a mark that stands on its own. Once you can read those codes, you can see exactly where marks come from and where you lost them.

This post covers the codes and abbreviations, checked against recently published Cambridge IGCSE mark schemes (Mathematics 0580, Physics 0625 and Chemistry 0620), plus the general marking principles on their front pages.

The layout: Question, Answer, Marks

Open any mark scheme and, after a few pages of front matter, you reach a table. The columns are usually Question, Answer, Marks and Partial Marks or Guidance.

• Question is the question number and part, for example 2(b)(i).
• Answer is the content that earns credit. It can be a final value, a list of acceptable points, or a method.
• Marks is the total for that row, often split into codes such as M1 A1.
• Guidance holds the extra notes: what else is allowed, what to ignore, and what to reject.

The row total matches the number in square brackets on the question paper. If the paper says [3], the row's marks add up to 3.

The mark codes

The number after the letter is how many marks of that type are available, so M2 is two method marks. In a mathematics scheme, A marks need the associated method mark to be earned or implied. So in practice an A mark cannot be earned if the method mark was not.

Some other subjects use the letters a little differently. A 0625 Physics scheme describes M as a method mark that must be scored before any later final answer (A) mark, and also uses C for a compensatory mark, which can be scored when the final answer mark was not awarded. A 0620 Chemistry scheme tends to label marking points M1, M2 and so on, where each one is simply the next thing to credit rather than a method in the mathematical sense. So the same letter can mean slightly different things. Check the notes at the front.

Dependency: why a right answer can still score nothing

This is the idea that catches most students. An A mark usually depends on the M mark before it. If the method was not valid, a correct-looking final answer does not rescue the A mark.

Mark schemes also use dep (dependent) to flag any mark that relies on an earlier mark. On the other hand, when a part has several method steps, the M marks are normally independent of each other unless the scheme says otherwise, so a slip in step one does not automatically wipe out step two.

B marks are independent. A correct statement or value earns its B mark whatever else happened in the working.

A worked example in the style of a mathematics scheme

This is an invented question, not one from a real paper.

Solve 3x + 5 = 23. [2]

Three students:

• Student A writes 3x = 18, then x = 6. Both marks: M1 A1.
• Student B writes 3x = 18, then x = 5. The method was valid, so M1 is earned. The answer is wrong, so A0. Total 1.
• Student C writes 3x = 28, then x = 28/3. The first step added 5 instead of subtracting it, so M0. The A mark depends on M1, so A0. Total 0.

In a real mathematics paper, a correct answer with no working may or may not score, depending on the scheme and on whether the question says to show working. The Physics 0625 principles say correct calculation answers get full credit even without working, unless the question says "show your working". Read the principles for your subject.

Follow-through, ecf and cao

FT means follow through after error. ecf means error carried forward. They describe the same idea: if you made a mistake earlier and then used your wrong value correctly in a later part, you can still collect the later marks, but only where the scheme allows it. The 0625 principles state that an incorrect answer subsequently used in a scientifically correct way should be credited.

cao means correct answer only. It is the opposite signal: no follow-through, only the exact correct answer scores.

If your part (a) answer was wrong, always carry on and use it in part (b). You may earn most of the marks in (b).

The other shorthand you will see

Verified in the published schemes named above:

• oe: or equivalent. A different but equivalent form is accepted.
• soi: seen or implied. The step does not have to be written out if later working clearly shows it.
• isw: ignore subsequent working. Once you have written a correct answer, a wrong tidy-up afterwards does not remove the mark.
• awrt: answers which round to.
• nfww: not from wrong working.
• SC: special case, a mark the scheme gives for a specified situation.
• owtte: or words to that effect, common in science schemes. Your wording can differ if the meaning is the same.
• ora: or reverse argument.
• Brackets ( ): words not explicitly needed, though a word that contradicts the bracketed one loses the mark.
• Underlining: the underlined word, or a synonym, must be present. If it is a technical term, that exact term is needed.
• / or OR: alternative answers, any one of which gains the mark.
• ignore: an incorrect or irrelevant point that is disregarded rather than counted as a contradiction.
• insufficient: an answer not worthy of credit on its own.
• CON: an incorrect point that contradicts a correct one, so the mark cannot be scored.

Any N from a longer list

A scheme row might say "any three from:" and list five or six points. You can earn up to three marks by making any three of them. Two further rules in the science front matter matter here. Read your answer as continuous prose, and if you give more than the required number of points, only the first allowed number are considered, and a contradiction can cost you. Writing extra points is not a safe way to hedge.

Alternative methods

For mathematics, the Cambridge principles say that unless a particular method has been specified, full marks may be awarded for any correct method. Do not worry that your route differs from the one printed. If a calculation is required, though, a scale drawing earns no marks.

What the general marking principles tell you

The front pages contain generic principles that every examiner must apply. Several are useful to know:

• Marks are whole marks only, never halves.
• Marks are awarded positively: for what you show you can do, with no deductions for errors or omissions.
• Marks are based only on what the mark scheme requires, not on grade thresholds.
• Spelling and grammar are only judged where a question specifically assesses them, though the meaning must be unambiguous.

In science, keywords used incorrectly do not score even if present, and a correct statement that is contradicted elsewhere in the same part does not score. Also, a missing or wrong unit normally costs the final calculation mark unless the scheme gives a separate mark for the unit.

Use your own mark scheme

Differences between mathematics, science and humanities schemes are real. Humanities papers such as Islamiyat or Pakistan Studies do not necessarily use M and A marks at all (some use levels of response or point-based credit), so check how yours explains its marking. The front page of each mark scheme includes the notes for that component.

Try it on a real paper

Pick a paper from the IGCSE Mathematics past papers or IGCSE Physics past papers, write your answers by hand, and see the official mark scheme beside your work. Reading and downloading papers and seeing mark schemes is free.

With a free account, ExamPal reads your handwriting and marks it against the official mark scheme, showing where each mark came from, including follow-through. For a method to do this yourself, see how to check your answer against a mark scheme.