Many aspects of tween development are the same for both genders, but there are some ways that girl behavior is unique from boy behavior. Here's an overview of girl behavior during the tween years.
Girls are more likely than boys to socially exclude a peer when they believe they may be ostracized themselves. In other words, girls often take action when they see a potential threat to their social standing; boys do not.
Full-blown eating disorders are rare during the tween years, but eating disturbances can arise, especially in girls. In fact, a quarter of tween girls report that weight affects their self-image and 13% say that they diet because of this.
Girls are more likely to experience early puberty than boys and for the early onset to have psychological causes. In addition, the effects of precocious puberty tend to be more severe in girls, with impacts on self-esteem, academics and body image.
While it's unclear whether girls actually use relational aggression more than boys do, we do know that girls use relational (social) aggression more than they use physical aggression. This is especially the case during the tween years.