In schools nowadays, to what extent of fist-fighting allowed without getting suspended/expelled?

Sorry to introduce a somewhat toxic topic. I have a nephew, 14 yo. He’s getting bullied by 1 or 2 students for being Asian, “nerdy”, blah blah blah. As a martial artist, I showed him some moves, counters, etc. That being said, in schools nowadays, to what extent can someone fight back/show people to not to fuck with them? Black in the day 15 years ago, if we had beef we just settle it during recess away from teachers, etc. I know violence isn’t the answer. I don’t want him going to the teacher bc he’ll be labeled as a “tattle tale”. In a way what’s a good balance between being physical to show people not to fuck with you vs getting suspended/expelled?