Off the dole, ten years later.

A CENTRAL precept of free-market economics is that incentives matter. If you raise the minimum wage, employers will hire fewer workers. If you raise the tax on income, individuals will work less. In retrospect, some of the most "radical" conservative policy innovations in history have simply attempted to align individual incentives with sensible social objectives.

One of the most controversial policies adopted in memory was welfare reform in 1996. An epidemic of single motherhood was one of the most pressing social problems of the late 20th century. Teens who had children were far more likely to drop out of school and live a life of poverty. Children of teen mothers faced disadvantages from the time they were born, when they averaged relatively low birth weights, through adulthood, when they were far more likely to end up in prison.

Until 1996, federal welfare policy perversely encouraged teen motherhood. A single mother could increase her welfare payment simply by having another baby. She could lengthen her stay on welfare by spacing her children out over time. The authors of welfare reform argued, quite controversially at the time, that these incentives induced young teenagers to have children out of wedlock. The echoes of the politically correct uproar that ensued still ring in the halls of the nation's newspapers.

But, against enormous odds, the 1996 reform finally reversed the pro-illegitimacy incentive. The bill required teen mothers under the age of 18 to stay with a parent if they received welfare support. It also hammered deadbeat ...