Haven't done it myself since my 18 yo home educated throughout opted not to do exams, but I've talked to a lot of people in and out of the system.
I've got a page on my website about home educators taking exams as private candidates with links to the home educators exams wiki and the yahoo support group for home educating families taking exams edyourself.org/articles/exams.php
Thanks Fiona, that is just the sort of info I was after. Flexischooling would work really well I think, with a mix of me and a private tutor or two covering the subjects not done at school. I'll be talking to the head next week and try to sell it to them. Knowing the thing about school registers looks pretty useful. She has done quite a few of the controlled assessments already, so, providing these can be transferred somehow to a friendly exam authority (and this needs to happen next week), homeschooling proper could work too.
DS did a kind of flexi-schooling in what would be Year 12 in England - he essentially just came home for one "column" of his timetable, to allow him to focus on a music qualification. The school were fine about it - we went in to discuss it with the Head, and I think his main issue was how to set it up without setting an easy precedent to let others ask the same. The things which I think helped to swing it for us were that -
1 - there would be an adult at home to supervise him 2 - he would be working towards a recognised qualification
That meant the school could have applied the same requirements to any other requests, and weren't opening the door too far!
It's worth thinking about it from the school's perspective - they will always be thinking more widely than what's best for that one child, because they have to weigh up how tricky it would be if lots of people liked the idea. So, as well as explaining why your child needs this, try to make sure you can show why the school won't have any difficulties if they allow it.