Back when I was a kid, if you had a problem with someone, you settled it with fists, then a few hours later, proverbially speaking the two of you'd be sharing a beer together.
Kids these days somehow have failed to learn this aspect of masculinity/humanity.
This can be fine with kids of equal physical stature, whether friends or a bully situation, but that's often not the case.
Martial arts training can be a great equalizer. Most folks don't know how to fight or stand up for themselves.
School was kind of like the prison system. If you perpetually got beat up you'd be labeled as a chump. Kick the crap out of one or two bullies and word would get out to not mess with you, and those that did were often alone as their friends were scared to have their backs.
I think a combination of both are what helped me out growing up as I was always one of the smallest kids in my class, as I was often a year younger than everyone else. Some of my friends, however, didn't fare so well, but they never stood up for themselves.