You would think, if lack of discipline is the basis, that you would see girls as well as boys expelled. Maybe misbehavior in boys tends more toward physical outlets that cause greater disruption to a classroom, while girl misbehavior is less disruptive on a classroom level? Or boys, due to their natural inclinations, more noticeably display the results of poor discipline? I think the best preschool for my boys is going to be one with an outdoor playground and lots of physical activity... I notice my older son's behavior is a lot better when he's burned off some of that energy.
I think a good part of it is the kids' diets. Filling them up with sugar-laden soda and snacks is going to cause hyperactivity in kids that age.
i don't know about the boy-girl disparity, to tell you the truth. but i do feel that people fail to parent their children nowadays and i fear what that will mean when they are grownups and peers of my kids. seeing how kids behave in public, mine will look at me and roll their eyes and say, some chance you'd have let us carry on like that.
Many of us remember a time when children did behave in school (and elsewhere) and teachers were able to TEACH. Teachers and students looked forward to a day of creative instruction with only limited interruption from a miscreant. Now teachers arrive at school defensive and antagonized. Creative lesson plans are useless if presented to an uncaring class. If I was teaching today, I would be tempted to buy body armor to wear each day.
So I don't fall for the "they are just being kids" theory. There was a time when (most) kids behaved. Unfortunately, we will most likely never see that again.
The best preschool for your child is HOME.