AS level

Introduced for first teaching from September 2000, GCE Advanced Subsidiary Level, can be taken as a stand-alone qualification or as the first stage in an A level course.

AS Level

First year of an A level course consisting of 2 or 3 modules. The modules can be cashed in to give an AS qualification or count as 50% of an A level. Module tests can be retaken to improve grades.

AS level

Examinations introduced in the UK in 1988 as the equivalent to `half an A level` as a means of broadening the sixth-form (age 16–18) curriculum and including more students in the examination system
Found on http://www.talktalk.co.uk/reference/encyclopaedia/hutchinson/m0018546.html
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