The worst teacher we had with DD2 (who has autism, inattentive ADHD and severe dyspraxia) was the school SENCO. This woman was the one who reduced DD2 from typing a page of good quality, well grammatically structured writing with a great vocabulary - to writing the date, title and one sentence in a ball of anxiety about the writing needing to be perfect or she'd be kept in for yet another break time to re-write it all. That damage took two years to undo. This is the one who introduced so many rules that DD2 was scared to ask to go to the toilet and sat in her own faeces as a result. We ended up moving school to get away from this woman and we were not the only SEN family that she succeeded in hounding out of the school.
We're lucky in that DD2 was that bit older when she had the ADHD diagnosis confirmed and DD2 is a massive massive people pleaser who wants to do the right thing and she was very aware that things wouldn't stay in her brain and it was hard for her to do things - and we have an amazing paediatrician who explained everything really well to her, and massively involved her in the diagnosis and titration processs - so DD2 has that feeling of ownership in her medication to the point that (she was 11 when she started on the medication and it was her choice to do so) she can tell you what period in school it kicks in and when it feels like its tailing off - we've got it so it kicks in during tutor time and starts to wear off during final less on the day so it's working well in that regard.
Pen licences - fuck those things - DD2 never ever got one, despite trying desperately, and DD1 got one despite having shit handwriting and not putting effort in - I hate them with a passion.
I'd try getting your son involved a bit - some form of a chart tracking when he takes his medication, how his brain feels when he does it, and how his school day goes (in terms of behaviour, pen licence shite etc) - see if he can make the connection himself with a bit of guidance from you (possibly use something like emojis for the ratings scales) and then at least he's making a decision with better information, or you've got some more information to take to your next review if things need titrating at all. If he has a run of days where he doesn't take it with a string of poo emojis or something similar - it might make the penny drop for him.
As for taking it everyday - we've been advised not to, we take it school days only - partly to reduce the amount of time she's taking a pretty potent drug, and partly to eek out supplies since the supply shortages still recur sporadically!