Oooo it's really tricky.
Honestly I wouldn't trust a teacher generally they know sod all about adhd (they couldn't believe my boy had it but it's so obvious now) equally I didn't initially want to medicate as I didn't want him like a tik - tak with loads of meds. But honestly it's helped him so much. Even if you only medicate only on school days - or trial it for a week or 2 and if it doesn't work you can always stop it at least you know - he might find life is easier with meds.
Also, consider if you or dad has adhd / ASD - all flows down through generations.
Keeping up the image - takes a lot of effort and pressure - maybe the older he has got the more work pressure / concepts getting harder so the effort to keep on top is tricky. ASD and perfectionism is a hard one to crack or the spoon theory.
I'd defo be pushing that senco ..... things move slow and when #### hits the fan things go wrong quickly. Then they get down beat and depressed - hard to pick them back up. So being able to adjust things and help b4 and develop coping strategies for your boy will help massively. Or trying to work out things to make his life easier at school.
Also, you might be allowed extra time in exams / laptops etc.
Never under estimate the school environment and people and NICE caring teachers are a massive thing - to really improve the mental health of the child .... so maybe he could chat to a nice teacher at school - for some bonding time. Equally if he's got a horrible cold teacher that he doesn't like that can make things a billion percent worse .... hopefully he's got a few nice teachers!
Rather than talking - my boys likes to write to me when he's upset / really angry (once he has calmed down) - it's more a informal way to communicate as he hates to have a direct conversation .... so maybe you could leave a note pad and see if writing helps .... who knows - just a suggestion
Suppose hormones are going crazy too.
Good luck