And parents play an equally important role. One of the best things you can do for your child's education/life is support the teacher when they call you up and say, "Your child is making poor decisions..."
I've known plenty of highly credentialed teachers that were very poor communicators and/or could not manage their classroom. I think the idea that this can be, or is, effectively taught as part of the "education major" is very suspect.
Indeed, the worst-performing school districts are precisely those where "classroom management" is a serious problem, versus better districts where the children come to school ready to be managed. It seems older styles of classroom management now out of vogue and untaught by universities were more effective.
Regarding managing kids...every school I've worked at (or my wife has worked at) has a mix of kids who are ready to learn and who need to be taught to learn. That includes districts in more wealthy areas and less wealthy areas.
In fact, my wife would tell you the students who cause the most problems in her classroom are from more affluent families. Why? Because they have entitled parents who don't hold their kids accountable and don't support the teacher.