Happened to me throughout my school life. I was forever picked on probably because I didn't know how to interact well with kids my own age. I was too used to adult company, and just too sensitive.
I admit even to this day I'm too sensitive. I still wouldn't know how to handle bullying if it ever happened again. As far as I was concerned nothing worked. Telling teachers only got me a fake apology from the bullies and even more teasing afterwords. Telling my parents only got me a grilling for not standing up for myself. But if I stood up for myself I got a grilling from the teachers. And I'd never even heard of a school cop, because there were none. I soon learned not to care about what my parents or teachers would do and decided that even if I got suspended I would always fight back whenever possible. (I went to one of those schools where misbehaved students got let off with murder while if a well-behaved student stepped out of line they'd be suspended) While all the time I only wanted to get on with my studies, I ended up a problem student with a ruined education.
For those who do bully, or have bullied: If you truly feel regret, then I think a sincere apology to your victims would really help. After leaving high school the bullies continued to haunt me, even though I never saw them again. I couldn't sleep, couldn't eat, I was just a total wreck because I couldn't shake it off my mind. Then I bumped into a group of them on the street one night. They started laughing and joking about me punching one of them one time back in high school and how much they deserved it, and how sorry they were for making high school a nightmare for me. I know it was no consolation for my ruined education, but you have no idea how this apology made me feel - it was like a huge weight had been lifted off of me, and from then on my mental state improved greatly. An apology can make a great difference.