But boys aren't the only victims—and they're not the only bullies. Rachel Simmons, author of Odd Girl Out, says girls are just as aggressive as boys, but they act out in much subtler ways. The effect of this "hidden aggression" is devastating to millions of girls but is often invisible to parents.
"Girls have a terrible reputation for being cruel, and there's a reason why," Rachel says. "They don't feel comfortable showing their anger directly. In order to deal with their anger, they go and tell someone else or they do it in a very sly way. They push their feelings down, but invariably their feelings come out in very secretive or indirect ways. So many of them are sitting on that anger. [Girls] do not have the tools to engage in assertive, direct conflict where they can actually say what's in their hearts to each other."