I know that school and exams can be worrying and stressful for parents of teenagers with eating disorders, not to mention for the teenagers themselves, so here's a bit of feedback I gave to another parent recently which may help other people too:
After a long period away from school in his GCSE year Ben decided to go back to school full time in the sixth form. From the start he pushed himself very hard - a case of 'all work and no play' which included avoiding his friends and over-working in the library through break, lunch and spare periods.
Not surprisingly by half term he had 'burned himself out', was hugely unhappy and so we had a re-think about a better way of approaching school which ended up being a case of Ben going in as and when he felt he could and doing work at home when he felt he couldn't. This way we hoped to gently ease him back into full days at school while getting him re-established with his peer group socially.
The previous academic year had seen Ben's descent into the eating disorder. By the February of GCSE year we'd decided to take him out of school altogether meaning that he studied for his exams from home. When it came to the exams themselves, Ben was allowed to sit them separately from everyone else with an individual invigilator. This way we avoided any problems of (a) Ben freaking out and ruining his own chances and (b) Ben freaking out and freaking everyone else out too! It worked very well. Also, because Ben was finding it impossible to be with his peers at the time, careful timing meant he never actually needed to meet other students: before, during or after his exams.
When it came to the AS level exams this year, Ben was well enough to sit them as normal with everyone else. The only problem was that he wasn't sleeping so was knackered throughout which has been reflected in his grades (his GCSEs were surprisingly good considering how little time he'd been in school that year...)
There was a 'Plan B' in place just in case he chickened out at the 11th hour; a separate exam room was available. But, in the event, he didn't need to use this.
Many of the ED teenagers I know of tend to be 'driven' to study hard for exams and get stressed out. Taking time out from school definitely helped things - plus the exam arrangements. And I never nagged him about revision or getting into school. Basically I didn't give a monkeys about the exam results; all I wanted was for Ben to get well and I made this clear to him throughout.
Oh, and the school was also able to arrange 'special consideration' for results that may be affected by the illness. It doesn't make a massive difference to grades, but can move things up a few per cent everyone at school feels the candidate 'could have done better'.
Basically what you need is a very supportive school. We were lucky in that respect and still are. Ben's AS levels were a bit dodgy, but he's being given the chance to re-sit them where necessary. Also, fingers crossed, he may actually make it back to school full time when term starts in a couple of weeks...