You can't even touch student and don't even think about slap. Some years ago I witnessed the case where teacher grabbed the student (14y old) who ran around screaming, kicking things and other students. A teacher was charged with a criminal offense (physical violence against a minor) and must now comply with behavioral supervision. What happened with kid? Nothing. He had a bad day and don't have skills to regulate his emotions yet.
For the rare few cases it may have been warranted, it wasn't a bad idea. The problem is that for the vast, vast majority of cases in which it was used, it wasn't warranted.
Remember: schools don't have tribunals to judge which student was or wasn't actually guilty of what, to which extent, with which attenuats if any, etc., to then decide who was going to be beaten and how much. The teacher merely looked at you, decided you were guilty because you didn't look into his eyes while he was speaking (autistic children were typical cases of this), and decided to traumatize you for life, fully unjustly.
When modern schools do the same but in the opposite direction, unjustly punishing teachers, that simply shows they haven't changed one iota from what they have always been.