My diary illustrates my perspective as a parent (a single parent at that), but I have noticed during the past few years how teachers are overwhelmed from all the reasons you listed in your post. I try to sympathize with them but it's harder to do that when trying to get the individualized education the government guarantees to disabled students regardless of funding levels.
I've noticed how all factors combined just make it easier for teachers to be drug pushers--suggesting, if not outright insisting, that the children having problems get on some sort of medication to cause the kids to (hopefully for the teachers) be more compliant. My son's schools always wanted to know if there was a pill he could take for his sleep disorder. Well, there is now, but that pill wouldn't have fixed his learning disability.
But that sure as heck didn't stop them from wanting to give him a pill. And when he was on some meds that helped in one area, they were unable to understand how that med could have an impact on another area.
Sadly, Bush and Big Pharma is only to happy to help get the schools involved in mental health screening and psychiatric med pushing, whether or not it's what the child needs or the parent wants.