One of the most studied initiatives in this area was the Perry Preschool program, which worked with disadvantaged black children in Michigan in the 1960s. Compared with a control group, children who went through the Perry program were 22 percent more likely to finish high school and were arrested less than half as often for felonies. They were half as likely to receive public assistance and three times as likely to own their own homes.

We don’t want to get too excited with these statistics, or those of the equally studied Abecedarian Project in North Carolina. The program was tiny, and many antipoverty initiatives work wonderfully when they’re experiments but founder when scaled up. Still, new research suggests that early childhood education can work even in the real world at scale.

Take Head Start, which serves more than 900,000 low-income children a year. There are flaws in Head Start, and researchers have found that while it improved test results, those gains were fleeting. As a result, Head Start seemed to confer no lasting benefits, and it has been widely criticized as a failure.

Not so fast.

One of the Harvard scholars I interviewed, David Deming, compared the outcomes of children who were in Head Start with their siblings who did not participate. Professor Deming found that critics were right that the Head Start advantage in test scores faded quickly. But, in other areas, perhaps more important ones, he found that Head Start had a significant long-term impact: the former Head Start participants are significantly less likely than siblings to repeat grades, to be diagnosed with a learning disability, or to suffer the kind of poor health associated with poverty. Head Start alumni were more likely than their siblings to graduate from high school and attend college.

Professor Deming found that in these life outcomes, Head Start had about 80 percent of the impact of the Perry program — a stunning achievement.

Something similar seems to be true of the large-scale prekindergarten program in Boston. Hirokazu Yoshikawa and Christina Weiland, both of Harvard, found that it erased the Latino-white testing gap in kindergarten and sharply reduced the black-white gap.

President Obama often talked in his campaign about early childhood education, and he probably agrees with everything I’ve said. But the issue has slipped away and off the agenda.

That’s sad because the question isn’t whether we can afford early childhood education, but whether we can afford not to provide it. We can pay for prisons or we can pay, less, for early childhood education to help build a fairer and more equitable nation.