Teenaged son doing GCSEs, struggling.

Hi,

my son is 15 and doing GCSEs next year; he got a late ASD diagnosis last year (a result of not being picked up at school despite our flagging things up and Camhs being totally oversubscribed which I'm sure is familiar to everyone). He masks a lot of the time and as he has very high targets at school he's fallen through the net. Over the past 2 years he has fallen significantly behind and he has stopped engaging with school. He does attend, though he's late every day and has a lot of sick days. He's just about to start end of year exams, and has done no work at all. I've started the process with the SENCO to get him an EHCP, but this will be too late to implement much before exams and the school have been helpful about putting some help in place in the meantime, but this is only just starting. He's getting some learning support to help him with planning and revision which is his main problem. I think he is presenting his best face at school, but in practice not doing any of the things he's being encouraged to do. He is extremely demand avoidant at home and if we even say the word 'school' or 'homework' he accuses us of berating him.  He's finally got some support from CAMHS after a 2 year wait as his moods have been very erratic.

I feel like I"m spending most of my time trying to access support for him, but when it's offered he doesn't engage with it and he has basically given up.

I know much of this is due to anxiety and processing problems but I am tearing my hair out; he's very bright and we're anticipating him not being able to take his GCSEs.  Does any one have any experience of this, or ideas about how to get him to engage with his school work without too much conflict, which is what seems to happen every time we try to talk about it. I know he can resit his GCSEs but I really worry about it, as he's very well developed and will be completely out of step with the other kids in his class. He's in a mainstream school.

I know what should be happening: supporting him with organisation, telling him we love him, which we do, and not making too big a deal out of exams (we try) but none of this works as he won't accept our help at all. As anticipated, an exam period has led to real volatility and then conflict at home as he's ground to a halt. 

Should we just accept that the he can't do and let him fail? this feels very hard to do.