Why is Ponyboy an outsider?

Ponyboy tells us in the novel "The Outsiders," that he is a member of the gang called "Greasers"  These guys are outsiders because they don't fit in with the group called the Socs.  The Greasers are from broken homes, poor economic situations and little education.  The Socs have the best of everything, which makes them more popular.  As Cherry tells Ponyboy,

"You greasers have a different set of values. You're more emotional. We're sophisticated—cool to the point of not feeling anything ... Rat race is a perfect name for [our life]." This leads Pony to wonder if perhaps it is just natural for the two classes to be separate and unequal—a fact that haunts Johnny's decision to turn himself in. He knows that the courts stereotype all greasers as juvenile delinquents."

Pony is also somewhat of an "outsider" in his own group.  He is younger than most of the other boys.  He is still in school and he is really pretty bright.  This causes a feeling of isolation for Ponyboy sometimes and he really doesn't understand the distance he feels.