The movie stereotypes of American high-school groups are broadly true except in reality these groups are not usually very hostile to each other. They tend to coexist peacefully. There is some friction, but
bullying is usually on a person to person basis rather than group to group.

The kids in Lewiston, Colorado ("Columbine" is the name of the high school) were sociopaths. Fortunately, such incidents are extremely rare. There are many millions of high school kids in America, and the number who shot their classmates or teachers over the past five or six years is probably about a dozen or so.