Talk to school authorities, really, this is not a behaviour, the child is so scared to even go to school matlab, talk to authorities n speak about the issue, say he's been hit by teacher n now he is afraid to go to school, request them to politely talk with kid n make him feel comfortable, don't make him sit home for very long time, his routine of going to school must not be disturbed.. for some time it's fine but not too long .. his mind should be set about going to school

But talk to the teacher too and firstly approach them politely n ask them to be little soft with the kid

The kid's mental state must not get affected

N clear them things about fault accusation as u said n of possible talk to the kid's friends too normally not to scold, just normally make them friends

Classmates ke saat normally speaking n asking name n apporaching n making them friends will help I guess

To talk the teacher and principal. You have a right to take appropriate action against them for violence. Go tell them you won't sit quiet. Your parents should talk to them. They'll warn their teachers out of fear of losing reputation of their school