Thank you so much, all, for these very helpful and encouraging replies.
music - my DS has been let down at his school - badly, I'm afraid, especially on the pastoral front. I'm very sorry to hear your story, though, and I do hope that your dd enjoys Chichester and can really look forward to a fresh start. What you describe is appalling. More and more I think that a school or college that is genuinely caring (in deed, not only in word) is worth its weight in gold. (It might not console your DD right now but some of the papers, notably the Independent, carried stories of teenagers who hadn't done at all well at AS and are now going, two years later, to good universities and courses etc of their choice.)
aig - you're right about the wide range of subjects at Havant - a student could put together a really balanced programme. That's probably its strength - I would hope, though, that there is good tutorial support for students.
Ilove - no, DS doesn't drive but I've also heard that Oaklands has a friendly sixth form -
badgers - thanks for mentioning Seaford. Our income is very modest but I could look at financial help there. I wonder if a number of 17 year olds enter the first year? That's something that would put DS off - he's super sensitive about repeating the first year of sixth form in a school especially although somewhere like Seaford might suit him - he's feeling pretty fragile at the moment.
badgerhead - thanks for mentioning The Weald - the fact that your DD could repeat modules as an external candidate is good to hear. Sounds like the school is very much more flexible than most. Probably a bit far for DS to travel each day, though.
DS worries that he's 'wasted a year' - hard to persuade a 17 year old that they are still so young with a lifetime of learning ahead of them! Will look now at Havant - and see what Seaford can offer - and, again, good luck to all our children and thanks again to you all.