Actually, forget what I just said. It looks as if I was wrong.
When we applied to a new sixth form mid-study, at the interview in May 2005 we were told that my son would not be able to resit his AS from the original board, once he had transferred to the new board. The Head of Sixth form said he had checked this and this was the case. We took his word.
We reluctantly decided to decline the place he offered at that very nice school, because it was not in my son's interests not to be able to resit.
However, a poster in this thread posted the link to the rules, and I have just read them for myself. They say something quite different:
"Where a candidate wishes to re-sit AS units, the centre must submit the JCQ Transfer of Credit form -
http://www.jcq.org.uk/exams-office/entries/gce-entry-information-incltransfer-of-credit by no later
than 21 October 2014. The centre must indicate on the form the series, i.e. June 2015,
in which the AS units will be taken.
• Where a candidate re-sits AS units with the original awarding body, after AS
certification in a previous examination series, he/she must claim their AS award(s)
again. This will ensure that the best total uniform mark will be available for transfer."
This means that resits of the AS level with the original board can be taken. I need to speak to this sixth form again, urgently!
Back to your original question:
You can transfer subject to approval from the new board. Transfers are not guaranteed. Each candidate needs to apply individually to each new board, giving details of what was studied for each AS with the old board. The new board wishes to ascertain that you will not be overlapping the content of AS from the old board to A2 at the new board. For example, you would not be allowed to have studied
The Tempest for English Literature AS with the old board, and study the same text for A2 with the new board.
Transfers are not allowed for the IB or for CIE:
"It is not possible to transfer components from an International Baccalaureate qualification.
• Similarly, it is not possible to transfer a completed AS qualification as awarded by Cambridge
International Examinations (CIE)."