It's hard for me now to remember the mentality of a 10-12 year old girl. I do remember, and I think it's important for everyone to remember, that for most pubescent girls, 12 and up, how powerful an effect rejection can have on these young girls. Just a sneer or an ugly look from a classmate can totally humiliate a young girl.
So I was bullied to a certain degree, and sometimes I would go along with the bullies and pick on other kids (on the school bus), or at least laugh at the poor kids. I seriously needed my tail whipped on a couple of occasions, and if I met any of these people today, I'd apologize profusely.
The main bullies in my particular situation were two girls in my neighborhood. One had an alcoholic father at home with a terrible temper, and the other had a mother who owned a bar and had a string of boyfriends (one of whom molested her) and left her and her younger sister home alone alot. Her older sister was well known as a slut. One time I and another friend were enjoying time off from school due to a big snow, and we found that bully's little 5 year old sister outside by herself playing in the snow with no coat, sweater or gloves on. Another time, this little sister's hair got so natty from never being combed that they cut it all off. Anyway, this particular bully was bullied herself by another group of kids, who would always call her mother a whore (she owned a bar frequented by prostitutes). The bully with the alcoholic father, she got sexually involved with a guy over 18 when she was 14 or 15, then after her parents divorced, she moved away and hooked up with this other older guy, had a baby when she was 17 and became an alcoholic. She ended up marrying this guy, having another baby, then she stopped drinking and got her life halfway in order.