To which the administrator of a good private school will reply, "the same thing a few hundred other parents are paying for."
"Unless you like to buy us a new auditorium, perhaps this school is not a proper fit for your child."
But what do you think happens to a teacher who keeps driving away paying customers because they have behavior problem children?
If the school is highly sought after in a high demand area then yes - they can effortlessly tell bad parents of bad children to take their money and go.
If the school is moderately sought after in a moderate demand area - and where you are offering a product that the government is giving away for ‘free’ - the economic reality is not so forgiving.
I have seen several “auditorium” parents - and it seems they WOULD rather buy a new auditorium for the school than to admit that their child is less than perfect and might need additional parenting and possibly even (gasp!) discipline.
“Unless you like to buy us a new auditorium, perhaps this school is not a proper fit for your child.”
Harvard and similar schools do have a special, but informal, admissions policy that works about like that :-)
(I’m not kidding, though)