Today, nearly half of American children born to parents with low incomes grow into adults with low incomes, and 40 percent of children born to wealthy parents become high-income adults. In the United States, which has based much of its social safety net on educational mobility, the ability to do better than one’s parents by completing more years of schooling did indeed rise between 1947 and 1977, but it has decreased sharply since.

Correlation of educational attainment between parents and children is now higher in the United States than in European countries, particularly Nordic countries, where a tiny fraction of low-income children becomes low-income adults. As Richard Wilkinson, coauthor of The Spirit Level, has said, “If Americans want to live the American dream, they should go to Denmark.”

Upward mobility has always been the exception to the rule — children born to families in the bottom income quintile have about a 6 percent chance of making it to the top income quintile in their lifetimes — but unfortunately it is a fantasy on which United States welfare programs are now based. Never has pulling oneself up by one ’s bootstraps been more plainly a cruel action than when prescribed as a policy regime for large swaths of the population.