The no smacking rule is flawed to start with. I remember my mother saying she never needed to smack me, and could not see why anyone should smack a child, then my sister was born.
There clearly needs to be control, we when I went to school had a punishment book, and only the head master, woodwork and metalwork teachers were allowed. It was considered safety first, and not to have the threat of the cain could result in unsafe practices by students.
Without the threat looking at exclusion, be it from school or a class, there is a balance, but in this case really nothing to do with school, she was the parent.