What "clans" are represented in Merryweather High School?
In the very beginning of the novel, where Melinda talks about her first day at Merriweather High she lists the clans as she sees them:
Jocks, country clubbers, idiot savants, cheerleaders, human waste, eurotrash, future fascists of America, big hair chix, the Marthas, suffering artists, thespians, goths, shredders. And then, of course there is Melinda herself- the outcast.
Melinda spends more time talking about the cheerleaders, the Marthas, and eurotrash because those groups directly involve her former and current friend(s).