AS and A-levels are taken in the two years of the sixth form (Years 12 and 13). AS-levels (Advanced Subsidiary levels) can stand alone or represent the first half of an A-level. In the second year of the A-level course (A2), pupils will study new topics, existing topics in more depth and there is some synoptic assessment.

Pupils take usually four AS-levels in the lower sixth, then take three of these on to A-level in the upper sixth − so they finish the sixth form with three A-levels and one AS-level. There are many exceptions: bright pupils may take a greater load (perhaps ending up with four or five A-levels); AS or A-level general studies is usually additional to the normal load; sometimes pupils will take extra AS-levels in the upper sixth; and a few schools save all the exams to the end of the upper sixth, so allowing the lower sixth to be devoted to teaching.

There are some 40 A-level subjects, both academic and vocational. Most sixth forms offer 20–25. There are A-levels in all the traditional school subjects (English, history, chemistry etc) as well as many others such as business studies, classical studies, media studies and psychology. Vocational subjects include applied business and health & social care, which are designed to develop skills, knowledge and understanding for the world of work as well as for relevant higher education courses.

Not all universities (or degree courses) accept all A-level subjects; their prospectuses may make it clear which are acceptable for entry and which are not. Some subjects are more widely useful than others and schools are generally good at helping match A-level choices with children’s post-school ambitions and personal aptitudes.

There are several examination boards that run AS and A-level courses. Each has different curricula so the schools can choose the one that suits them best or that they prefer to teach – and can choose different boards for different subjects. Passing grades for AS levels range from A (highest) to E (lowest); for A-levels A* to E.