Since at least the days of Horatio Alger, a cornerstone of American thinking has been the hope of social mobility—the idea that, as Lawrence Samuel put it in a history of the American dream, anyone can, “through dedication and with a can-do spirit, climb the ladder of success.”
In recent years, though, plenty of Americans have come to believe that, as President Obama said in his State of the Union address, “upward mobility has stalled.” So it was a surprise recently when a team of economists from Harvard and Berkeley released a comprehensive study showing that mobility in the U.S. hasn’t fallen over the past twenty years at all. “Like many people, we thought mobility would have declined,” Raj Chetty, one of the researchers on the project, told me. “But what we found was that kids born in the early nineteen-nineties had the same chances of climbing up the income ladder as kids born in the seventies.” Even more striking, when the researchers looked at studies tracking economic mobility going back to the fifties, they concluded that it had remained relatively stable over the entire second half of the twentieth century.
That sounds like good news, but there’s a catch: there wasn’t that much mobility to begin with. According to Chetty, “Social mobility is low and has been for at least thirty or forty years.” This is most obvious when you look at the prospects of the poor...