Take it from someone who dealt with bullies nearly their entire Schooling, peaceful conflict resolution does not work with these types of narcissists that actually makes them worse the best way to stop a narcissist / bully is to roast them or beat their ass.

Both are good methods. Your sister did a good thing. The school is just being petty and idiotic for tryna punish him when defending himself against a BULLY. The bullies should get in trouble, not him. He should also learn to use his fists as well. Trust me, as a victim of bullying for so many years, he has to learn to use his fists along with his wits.

Your son has a bright future no matter what some out-of-touch administrators and hands-tied teachers say.

Your son has become a bully. If your son used his new-found verbal abuse skills to neutralize a physically violent bully, that would be justified. But if he's unleashing his weapon on other kids, then your sister created a monster.

As a former bullied kid who was repeatedly taught “peaceful resolution”: it is about as useful as a chocolate oven tray and leaves a way bigger mess. Good on your sister for teaching your kid a successful way of getting the bullies off his back.

If the principal did nothing when your kid was getting bullied but suddenly feels that this is something they need to deal with, you need to ask your sister for some tips on how to make the principal cry too.

No, absolutely let him fight back. Go in to see the principal, and directly ask why nothing was done about THEM bullying but now that your son is handling it, NOW it's a problem. Good on your sister. "Peaceful conflict resolution" doesn't do shit on bullies

See the principal for what? For an apology from the bullies who have been harassing your son, and an apology from the school for not taking care of it before it came to your son dunking on them until they cried?