How to deal with stone-throwing kids

Two months ago, we got a call one day from one of my children's school. One of our children, we were told, had been throwing rocks at passing cars, and could we please come get him. My oldest child is 27, so I have had children in school for a long time. This was the first time we had ever been called to school to pick up a child. We would have read the child the riot act (and the principal did