The Advanced
Subsidiary Level qualification, it is essentially half an
A Level (The voluntary and free*
UK qualification, generally taken after
high school as a gateway to
university). It is a qualification in its own right, and since September 2000 it is required to do the AS Level in any given subject that you want an A Level in. After the AS Level is completed you have the
choice of doing the
A2, completion of the A2 in a subject grants you the A Level.
This means that if you drop out after one year you can still walk away with some qualifications. It does mean however that there is a slight increase in the work load.
*Bariau reminds me that nothing in life is free, but if you take the A-levels as a young person you don't have to pay