As I recall, your kid's not that old.
Possibilities: He's bored, or he's upset about something. Or, he senses he can get away with it with that teacher.
Asking him why he's doing whatever it is would be a good start. If it's something like a bully or he can't see the board or understand subtraction, you can work on the problem with him. If it's boredom or smart-aleckiness, going over the rules, as if he didn't know them - once - is good. Letting him know that any more infractions means a loss of all privileges, or at least that one thing he loves most, for X amount of time, and starting the time over for each subsequent infraction. (That way, he doesn't end up with such a long penalty he can't ever get it back.) If there is nothing like that, give him a chore he hates till he straightens up, like cleaning the cat box every night or even sentence writing. That was the punishment my nephew dreaded most, even into junior high!