The traditional story of economists has been to say education explains what the returns are to school. I say, 'Okay, that's fine, but what explains the education? How much is just a matter of my giving you a poor kid versus a rich kid?'

Some kids win the lottery at birth; far too many don't - and most people have a hard time catching up over the rest of their lives. Children raised in disadvantaged environments are not only much less likely to succeed in school or in society, but they are also much less likely to be healthy adults.