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Many girls around the world routinely experience school-related violence that puts their physical and psychological well-being at risk, undermines their opportunities to learn, and often causes them to drop out of school entirely. Schoolgirls may be raped, sexually assaulted, and sexually harassed by their classmates and even by their teachers. They may be targeted because of their sexual orientation or gender identity. In situations of armed conflict, insecurity and attacks against schools may keep girls out of school altogether. 

Human Rights Watch investigations have documented sexual violence against girls in schools in Zambia and South Africa, the impact of insecurity and attacks on schools on girls' education in Afghanistan and Iraq, and harassment and violence against lesbian, bisexual and transgender students in the United States. 

Girls are at the brunt of it, but a number of boys get bullied as well for not falling in line.

To some extent there is a gender component, but to some degree it's about an obsession with violence.  Both must be considered.  And there are probably more contributing factors, as well.