Author and educator, Rachel Simmons, could never understand why at just 8 years old, a "friend" convinced other girls to run away from her after school. In college, she discovered that all of her friends had similar "mean girl" stories from their childhoods. And so she began to interview women on the subject and wrote a book, Odd Girl Out, exploring the psychological aggression between girls.
In the clip above, from the documentary, MAKERS, Simmons explains what she discovered about why girls behave aggressively towards each other. "Girls know they have to maintain an exterior of happy, peaceful relationships and kindness, and yet they have to do something with their angry feelings," she says.
Simmons also emphasizes the importance of parents' involvement in their girls' friendships. Studies have shown that when mothers intervene, their daughters are less likely to use friendship as a weapon, she says.
Watch the video above to hear Simmons' message for girls, and tune in for the entire MAKERS film on Feb. 26 at 8 p.m. ET on PBS.