I know American culture and society champions the individual and individualism, to a greater extent than here, so it doesn't seem much of a stretch to assume that such conditioning begins in school, or even earlier.
I used to watch shows like 90210 with a certain fascination, wondering if the "kids" were really as mature as they seemed, grappling with what to me seemed like adult problems.
You have the football jocks and prom queens and what must be a mass of average students and kids, but it then seems like the "nerds" and "geeks" who don't fit in there, are going to be significantly more marginalised than their equivalents here. And I was very much a nerd myself. That always has the potential to be deadly in a gun obsessed society.
I hope it's clear that I'm not trying to provide a justification of such warped behaviour, just trying to understand within the context of what seems to be as a very damaging emphasis on individualism in the US.