A new subject-by-subject guide lifts the lid on A-level grades and spells out exactly what students have to do to pass.
The Qualifications and Curriculum Authority (QCA), which drew up the guidelines, said they would help people to discover what the A-level "gold standard" meant in the real world.
In modern languages, A-grade students have to write fluently, using a wide vocabulary with few errors. They must convey concepts and opinions clearly and with ease. An E-grade candidate, by contrast, will use an appropriate but unsophisticated style, and include "some very basic errors".
In history, E-grade candidates must "demonstrate awareness that historical events, topics and individuals have been interpreted in different ways", but can "offer conclusions which may be underdeveloped or largely unsubstantiated".
To get an A, however, the arguments have to be "well supported and balanced judgements about these interpretations which are communicated with clarity and precision".
Each document spells out in detail what examiners expect from A-level courses in each subject and makes it plain that students who pass must gain a thorough basic understanding.
The standards, which have been written to cover 27 major subjects, are used to check exams covering the hundreds of different A-level syllabuses.
A spokesman for the QCA, which regulates all public exams, said: "The criteria represents the gold standard. This makes clear the difference between a grade A candidate and a grade E candidate."
John Dunford, general secretary of the Secondary Heads Association, said: "This is useful if it opens up the secret garden of the curriculum, but teachers can predict people's grades accurately using their years of experience after looking at their work."
George Turnbull, spokesman for the Assessment and Qualifications Alliance, one of the three major exam boards for A-level, said: "There's something missing in a qualification if you can't say what you expect of people with a certain grade. It's an essential part of the process."