To me, the UK school system is teetering on the edge of breaking down. Some people react to this by blaming the students. Others blame parents. Yet others blame teachers. But it's a system-wide problem. It needs to be fixed from the top down.
The school environment, as it stands, is absolutely the wrong place for a certain % of students (most of these are SEN). But there are very few alternatives for those SEN students, and none are easy to access. So you get a LOT of SEN kids limping along in the current, one-size-fits-all system, and you get staff without training deciding that the best way to deal with them is punishment or more punishment. Meanwhile, the staff have OFSTED hanging over their heads so they're stressed about forcing students to meet arbitrary targets (thanks to that Pob-wannabe Michael fucking Gove and his "reforms"). And the system isn't funded well enough to deal with different types of learning styles, so thirty kids are lumped into one classroom, and if they don't learn well that way, some people accuse them of "not wanting to learn or succeed!" and hand out more punishment.
It's depressing. I feel bad for teachers and I feel bad for students.
But I'm also very tired of people defending the status quo. It's broken. UK teenagers are switched-off and unhappy. It's all very well saying "we must enforce rules" but then we see people like Boris Johnson getting away with partying during lockdown, and Michelle Mone walking away with a whole bunch of taxpayer £, and if there are no repercussions for the top echelon of people, then it does make me wonder why some people here froth at the mouth so hard to give little Johnny a detention for forgetting a green pen, because "rulez is rulez".
OP, I'm parenting a (suspected) ADHD child, too, and I'm reaching breaking point. My autistic child had a very supportive secondary and he's currently flying in sixth form having gotten great GCSEs. My younger one has an unsupportive school who is currently refusing to fill out the Conners questionaire to help her get an ADHD dx. This after refusing to refer her to CAMHS in the first place (I had to approach a GP). No real reasonable adjustments (they want a dx first).
Anyway, I'd advise you to pick your battles but prioritise your child's mental health above all. Because the system sure bloody won't.