The Outsiders is what's known in fancy literary circles as a Bildungsroman, a German term that literally translates to "novel of education" (source). This usually refers to the main character's journey toward self-discovery, and discovery of his or her place in society. Ponyboy Curtis, our protagonist, definitely fits this bill. The novel also examines inequities in educational opportunities due to social and economic factors. Both of Ponyboy's older brothers have had to limit their educations in order to work and support their family. And Ponyboy also feels like lots of teachers are prejudiced against Greasers. But it's not all bad. Ponyboy's English teacher, Mr. Syme, doesn't see things in "Greaser" vs. "Social." He recognizes Pony's talent and takes into account all the trauma his student's been subjected to and how this might impact his performance in school. Then Mr. Syme gives Ponyboy a writing assignment that really helps Ponyboy develop as a person, the assignment which turns into the book we're reading, The Outsiders.
In The Outsiders, Hinton works hard to show that even though lower-income people might be less educated than their wealthier counterparts, it doesn't mean they're less smart.
In The Outsiders, it is mainly through the tools provided by education that Ponyboy is able to break down boundaries and connect with others.