A: Your question indicates a degree of indecision that may be clouding your judgement. I think you need to think beyond this move and ask yourself where you want to see yourself in, say, five years' time.
Doing the same job in another setting for a couple of years might be a good idea. It broadens your experience, which might then help you gain a head of English post at an 11-16 school.
I think you would need to consider whether an AST post would be a sideways move if you want to end up in a leadership job.
The grade was designed for those who want to stay with their subject, but it is difficult to see where one can go afterwards except into areas such as the advisory service. Other possibilities, such as teacher training, might mean a drop in salary compared with even the middle of the AST range.
You also need to consider whether it might be worth applying for a head of department post, rather than an assistant headship, given you are looking to take a step up
John Howson is a recruitment analyst and visiting professor of education at Oxford Brookes University. To ask him a question, email him at firstname.lastname@example.org.