A. Your first duty must be to the pupil and, assuming that he is under 16, it would not be reasonable simply to order him off the premises. I suggest that you ask the education welfare officer to escort the boy to his home so that he can be returned safely to the custody of his parent.
If the parent is not there, it may be necessary to detain the boy either at school or at the education welfare office until such time as he returns. The parent must be informed by the education welfare office and by letter that his conduct is unacceptable and prejudicial to his son's prospects.
If he persists in bringing the boy back, you may have to resort to treating the boy as a trespasser and asking the police to remove him.