From your recent updates it really looks like the fact that his day and night are dysregulated that are the major problem - of course he can’t manage to go to school if he has not slept all night!! Could you talk to him, on a very practical level (getting rid of all emotion / judgements about ‘laziness’ etc) and say that his exams will be during the day (some of them will likely start very early, maybe 8.00 / 8.30am), so you and he need to come up with a way to gradually shift his sleep / wake patterns, so that he is actually sleeping at night, before his exams (and actually sinner than that, eg starting the process tonight!!). If he tries to sit exams after a night of being up, that will be a complete disaster.
It sounds like he has a lot of potential, and it would be such a shame if he did not put things in place to try and meet that potential. You need to get his agreement to a staged process on shifting sleep / wake patterns. Does he have tv / gaming in his room? Could you see what he thinks about how to reduce the amount of time he is spending watching screens over night?
Are you working at the moment, do you have anyone else around that can support you? Essentially, (as an outsider), i think the first step might be to limit the amount he can sleep in the daytime, so that he starts to build up ‘sleep pressure’ in the night. When does he typically start to sleep at the moment, and when does he usually wake up? You need to get him up earlier?
If he goes to sleep at 5.00am - 6/00am, maybe only allow him 5-6 hours of sleep in the morning, so make him get up at 12 noon (?). And do not let him nap or sleep later in the day. (He needs to build up ‘sleep pressure’ - that feeing behind your eyes that you are tired and really need to sleep, this triggers sleep hormones.. if you nap in the afternoon, the sleep pressure goes, and you can’t sleep at night…).
Then the next day, ask him to go to sleep by 2.00am (is he 18? Maybe get him some herbal Nytol to take beforehand, it can be quite effective at making you sleepy). And get him up at 9.00am the next day. And don’t let him nap!!
Then get him to go to bed at midnight, and get him up at 8.00am. And no napping!
Then get him to bed at 11.00pm, and get up at 7.00am. And the try and get him to keep fairly consistent timings. And no napping!!
If it was me, I would try and move screens out of his bedroom.. (I think ND teens can really develop a dependence on them), so he does his watching films etc downstairs… I know this would be a difficult one though. But it could really help. Maybe frame it as ‘sleep hygiene’ so it is not a criticism of his habits (google ‘sleep hygiene’ habits, there are tips for making your bedroom a relaxing space for sleeping, and routines to help you calm down. Having a bath or shower on evening can help (apparently the core body temp dropping after bath / shower can also trigger sleep hormones).
Maybe he doesn’t want to engage because he feels that ‘everything is lost’ (re: his A levels). But it definitely isn’t. He sounds like he could do well, if he spends some intensive time practising his language A level, and the one that you said was easier. Definitely try and get additional tuition if you can.
Can you throw a lot of effort / resources at this? Can you be around (away from work) over the next week while he re-sets his sleep / wake times? Can you get extra tuition, or find extra resources online? Or sit there and test him (over the next few weeks) or compile comprehensive revision notes from ChatGPT? ‘Save my exams’ is a great website with practice papers, full revision notes, practice questions etc, worth taking out a 3 month subscription if you can.
A shorter amount of Smart / efficient revision is worth many many hours of inefficient revision. He needs to do some gap analysis, identify where he can make the most difference, and really really look into exam technique, for each exam. There are great YouTube videos from teachers out there.
You need to tell him he is at a cross roads - he is very intelligent and capable, and shouldn’t let himself be held back by lack of confidence. The choice he makes now - today - is really important. If he takes on the challenge, he can make great improvements in a short amount of time. He should not aim for perfect grades - he should aim to achieve as many marks in his exams as he can - and every single extra half hour of revision he can do, can get him extra marks.
Have you looked at the grade boundaries for his subjects, and his exam board, for last year? The year my eldest dc sat A levels, you only had to get 51 or 52 % correct, to get an A (in physics). I just couldn’t believe it - you could get nearly half of it wrong, or be unable to do nearly half of it, and still come out of it with an A.
It is so so worth him giving it his best shot, and seeing what he can do.
And see if he will trial other adhd meds, as pp’s have suggested - maybe do some research online about this (there may be some forum posts somewhere (maybe Reddit?) which talk about experiences of different adhd meds, and how side effects can vary.)
Sorry for long post - and good luck!!!