A kid bullied me in first grade, but after some encouragement from my mom, I stood up to her and was rarely bullied after that. There were some mean 'rich' kids in sixth grade (the joys of busing ) that bullied me pretty relentlessly, I assume because I was quiet, poor, and dressed like a dork and I had trouble figuring out how to handle that. I could handle the overt physical intimidation better than the more subtle, verbal stuff. Funny because I, like Lat, was usually the youngest kid in my class along with being very small for my age. It's just that when people try that stuff with my, I go kind of crazy and it I guess it sort of catches people off guard.
As far as my kids go, I try to suck up to the powers that be at their schools in advance so that I already have some kind of rapport. I expect my kids to try telling the adult in charge, but if that doesn't work, I talk to the school and they do usually take care of things. So far they haven't had to resort to defending themselves, but they have my permission to do so, should the need arise.