I remember in grade 3 & 4, there was this one guy who used to pick on me mercilessly. Beating me, tripping me in class. He even used to beat up guys in grade 6. The teacher used to give me a ride home, 'cause the guy would wait for me (she had nice legs, LOL). The principal tried everything, but the kid wouldn't stop. The kid's parents couldn't do anything. Other kids were afraid of him, so they wouldn't help, then they would join in sometimes also. Finally, one day, I'd had enough. I guess I lost it, I don't remember, but I remember chasing him home & him being all bloody. The principal called my Mom & everyone was actually happy about it. It was good that I stuck up for myself, but sad that he couldn't stop before pushing a shy passive guy into that kind of response. The poor kid actually got killed a coupla years later, 'cause he wouldn't do as he was told & his Dad backed over him with a horse trailer.

There were others over the years, but that was the worst, & the beginning of my lack of tolerance for bullies.
On the other hand, you have to watch kids that were bullied, because often they turn into bullies themselves. I did with one student in grade 9, but I realized what I was doing, sincerely apologized, & we actually became friends, of sorts. I look back with deep shame on this incident.
Sorry to hijack your thread.