how are groups identified and by what charateristics are they identified? how does their belief and identity affect their decisions?

The "Plain Janes," I think this name speaks for itself.

One group is the Marthas; they are dedicated to charity and decorating for school dances and special activities.

"My first day of high school and I can see, as we are herded into the auditorium for orientation, that I don’t fit in. Everyone else falls into a clan – you know, a clique; THE JOCKS, THE CHEERLEADERS, FUTURE FASCISTS OF AMERICA, GOTHS, …well, you get the idea."