“If I were the principal, I would have said to the bursar, “Rabbi so and so, I understand that you would like the children of Mr. so and so rounded up like criminals and sent home. Please go round them up yourself, or have your assistant do it. I am not going to take part in being mevayesh these little neshomos over money.””
Then the principal would lose his job. If no one was willing to do it, the school would close and no one would have a school. That may be better than embarassing a child, but the money must come from somewhere. Some chovos (electric, insurance, etc.)(teachers!) must be paid or the school will close. If this is a way to get the parents to take responsibility and raise the money (via a Tzedaka drive, possibly (as I have seen done)), this may be the only way.