Sorry, Wikipedia doesn’t meet the standard of “basic research.”
Of course, none of this discussion of abuse has anything to do with the original topic. I see nothing wrong with a teacher showing physical affection for a child (pat on the shoulder, maybe even a hug), but only in the presence of another adult and only if it’s clear the child will benefit from it. To make it contemporary, suppose a child’s house has been destroyed by a hurricane. He comes to school, obviously very upset. He needs comforting. If he has a good relationship with a teacher, the teacher is an obvious person to comfort him. For some kids, some physical contact is the most effective method of comforting him.