If what you’re referring to is behavioral problems, the more obvious explanation to me is that as kids spend less and less time being physically active, they become more restless and feel under-stimulated when they have to sit in school all day.

Kids with diagnosed or undiagnosed Autism didn't used to stay in the same class as "non-disruptive" students, oftentimes not even in the same school. But it's so much better understood now that there is a much stronger effort to keep the classes as integrated as possible and just figure things out as they present. But the problem is that it's being compounded by spending cuts that have led to integrating even more than what currently makes sense because they can't afford enough teachers to split classes more. Instead, they hire cheaper teachers assistants and try to handle 30+ kids in the same room. A teacher and 2 TAs for 30 kids is a much worse situation than 2 teachers with 15 kids each.

When I was in school, even my, at the time called Asperger's syndrome, was enough to have me pulled out into a side class with a specialised teacher. That side room was 10 kids and had 2 TA's as well. They managed to keep that room so well organised that I was able to pull ahead a grade in that environment. Partially just due to not having to wait for all the other kids in the bigger class to learn stuff before I could move on. Each kid in the 10 kid side-class was on individual learning. So I could breeze through all the stuff I found easy to have more time to work on the stuff that was unduly challenging for me.

On the neurodivergent version of the IQ test they had me do back then, my section scores varied from as low as 74 in a section to 152 in my highest, averaged out to 121 overall. So there was more that I was good at than bad, but 74 is pretty low, so I had to spend a lot of time on that stuff. And it's tough, the brain hates doing stuff that is relatively challenging. But they worked out a sort of interval training reward system that worked for me. I guarantee I am a much more useful person to society now than I would have been without the funding schools used to have. I shored up my weaknesses while still building my strengths.

After a year in the side course, I was able to rejoin the main class, but a grade higher than the class I used to be with before. The school got me a personal education assistant to keep me on task through challenging stuff or boring stuff. Anything that would otherwise cause my mind to wander or seek out other activities. Eventually, with practice, I was able to keep myself in check with the same tactics.