I dont have kids but it wasn't that long ago I was one
. And I have had lots of experince with kids.
Nomather what happend you dont choke a kid. If he has a gun, call the cops. If he tries to beat you up. Then just take a firm grip and get him to calm down.
If that teacher is strong enough to get the upper hand on the kid then he sure would be able to keep him calm even if the kid (i'm not saying he was) was pissed like hell and just wanted a to kick some butt.
When I where young I often got in trouble and tried to beat up a couple of teachers but they never hit me. They just hold me so I couldn't make any more trouble and now I understand that this was the best thing for me.
If you beat a kid that is out of line he will most likely get more pissed and come back for more. But if you can get him calm and talk to him he doesn't get that "I'll kill you for beating me up" feeling.
So the teacher where wayyy out of line when he choked your kid.