In the same way that you don’t notice the specifics of your own culture until you travel elsewhere, you don’t really notice your social class until you enter another one. As an undergraduate at Yale a decade ago, I came to see that my peers had experienced a totally different social reality than me. I had grown up poor, a biracial product of family dysfunction, foster care and military service. Suddenly ensconced in affluence at an elite university—more Yale students come from families in the top 1% of income than from the bottom 60%—I found myself thinking a lot about...