AROUND 1970, psychologist Walter Mischel launched a classic experiment. He left a succession of 4-year-olds in a room with a bell and a marshmallow. If they rang the bell, he would come back and they could eat the marshmallow. If, however, they didn't ring the bell and waited for him to come back on his own, they could then have two marshmallows.

In videos of the experiment, you can see the children squirming, kicking, hiding their eyes -- desperately trying to exercise self-control so they can wait and get two marshmallows. Their performance varied widely. Some broke down and rang the bell within a minute. Others lasted 15 minutes.

The children who waited longer went on to get higher SAT scores. They got into better colleges and had, on average, better adult outcomes. The children who rang the bell quickest were more likely to become bullies. They received worse teacher and parental evaluations 10 years later and were more likely to have drug problems at age 32.

The Mischel experiments are worth noting because people in the policy world spend a lot of time thinking about how to improve education, how to reduce poverty, how to make the most of the nation's human capital. But when policymakers address these problems, they come up with structural remedies: reduce class sizes, create more charter schools, increase teacher pay, mandate universal day care and try vouchers.

The results of these structural reforms are almost always disappointingly modest. Yet policymakers rarely ever probe deeper into problems and ask the core questions, such as how do we get people to master the sort of self-control that leads to success? To ask that question is to leave the policymakers' comfort zone -- which is the world of inputs and outputs, appropriations and bureaucratic reform -- and to enter the murky world of psychology and human nature.

Yet the Mischel experiments, along with everyday experience, tell us that self-control is essential. Young people who can delay gratification can sit through sometimes boring classes to get a degree. They can perform rote tasks in order to, say, master a language. They can avoid drugs and alcohol. For people without self-control skills, however, school is a series of failed ordeals. No wonder they drop out. Life is a parade of foolish decisions: teenage pregnancy, drug use, gambling, truancy and crime.

If you're a policymaker and you are not talking about core psychological traits such as delayed gratification skills, then you're just dancing around with proxy issues. The research we do have on delayed gratification tells us that differences in self-control skills are deeply rooted but also malleable. Differences in the ability to focus attention and exercise control emerge very early, perhaps as soon as nine months. But there is no consensus on how much of the ability to exercise self-control is hereditary and how much is environmental.

The ability to delay gratification, like most skills, correlates with socioeconomic status and parenting styles. Children from poorer homes do much worse on delayed gratification tests than children from middle-class homes. That's probably because children from poorer homes are more likely to have their lives disrupted by marital breakdown, violence, moving, etc. They think in the short term because there is no predictable long term.

The good news is that while differences in the ability to delay gratification emerge early and persist, that ability can be improved with conscious effort. Moral lectures don't work. Sheer willpower doesn't seem to work either. The children who resisted eating the marshmallow didn't stare directly at it and exercise iron discipline. On the contrary, they were able to resist their appetites because they were able to think about other things.

What works, says Jonathan Haidt, the author of "The Happiness Hypothesis," is creating stable, predictable environments for children, in which good behavior pays off -- and practice. Young people who are given a series of tests that demand self-control get better at it.

This pattern would be too obvious to mention if it weren't so largely ignored by educators and policymakers. Somehow we've entered a world in which we obsess over structural reforms and standardized tests, but skirt around the moral and psychological traits that are at the heart of actual success. Mischel tried to interest New York schools in programs based on his research. Needless to say, he found almost no takers.