If one can hit when not angry and only wants the best for the child (and not just convincing themselves otherwise), then it should be ok… the problem is that many rebeim have too much gaaiva and do not know how to control their anger…
Teachers need to know how to answer their students… I was in a class where a child asked an on-topic question that was just a little different from the mainstream view of the class (the kid thought for themself and added up what the teacher said and came up with a decent question..). The teacher did not know the answer and said “next question please” and was visably upset. If you do not know a topic- dont bring it up to the class! Answer the questions and if you dont know- say so and “Ill ask someone else and bring you back and answer…” Show that there are answers but the teacher doesnt know everything. Teacher who do not admit their mistakes lose credibility with the class and shows that they can turn to violence… dont just hit the student (physically or verbally)!!!