That's the impression I have as well, but I am also cautious about accepting it. People tend to discuss the bad schools and ignore the good ones. They tend to focus upon the families who don't care for their kids (may they be poor or rich), and ignore the families who do care for their kids. It's easy to understand why. The kids who do act out need a disproportionate amount of attention to keep the system on track.
The negativity bias is a good point.
I wonder if it isn't so much the absolute number of kids who act out (at least initially) so much as it is the change in the way we've handled consequences? My understanding is in a lot of school systems, it's nearly impossible to hold a child back or to fail them, and that it's much harder to mete out discipline. Even if the number is holding steady, the rest of the class/families are still seeing that there are no consequences for not meeting standards and exhibiting problematic behavior, which is sort of the start of a slow moving poison.