One of President Obama's favorite causes is universal pre-K school that is free (except to taxpayers), which he touts as a cure to inequality.

Indeed, pre-K is dear to the hearts of progressives such as Mayor Bill de Blasio and even Our Kids author Robert Putnam.

That we've in effect had free, pre-K for many years in the former of the Head Start program and that its results have been shown to be at best ephemeral does not dampen their enthusiasm.

Now, the Manhattan Institute's Kay Hymowitz has happened upon evidence that another famous pre-K experiment didn't work.  She "stumbled on" a study of graduates of the Perry Preschool experiment, always cited by advocates of government-paid pre-K, forty  years on.

The Perry Preschool was an experimental program for 123 poor African-American kids in Michigan between the years of 1962 and 1967. The children were three and four years old, who were randomly separated into two groups. One group spent two and a half hours a day with teachers who a bachelor's degree or more and used a special curriculum. Parents were involved through counseling and frequent visits to the school. The second group were pretty much left alone.

The research indicates that Perry graduates of the group that received special treatment did indeed benefit. Eighty-eight percent of the female children in this group went on the get a high school diploma, compared with  46 percent of those in the other group. These girls were less likely to become pregnant.

The Perry boys also showed benefits, though not as dramatic. Fifty-four percent obtained high school diplomas, compared with forth-three percent of those in the group not exposed to special treatment. They also committed fewer crimes, another big benefit.

So what's not to like?

Hymowitz looked very carefully at the celebrated results and found that as the Perry kids grew up, the benefits were there but not as significant as one might think from the hoopla:

But—and you will almost never see this caveat in the thousands of celebratory references to the program—the best that can be said about the Perry kids is that they wound up less poor than their untreated peers. At age 40, those in the treatment group had median annual earnings (including benefits) of $20,800 (in 2000 dollars), versus $15,300 for the untreated. That’s a substantial difference but not enough to take the Perry grads out of the ranks of the “near-poor,” as conventionally defined. (The poverty threshold for a family of four in 2000 was $17,603; “near-poverty” is defined as between 100 percent and 125 percent of the poverty line.)

Nor is that the only reason to temper Perry-based hopes. The nontreatment-group women, who were more likely to become teen mothers, had higher rates of welfare dependency before age 26. But there were no significant differences in the overall nonmarital birthrates between the two groups—and by 40, female Perry grads, who tended to become mothers in their later twenties, surpassed their nontreatment peers in welfare dependency and nonmarital childbearing. Half of treatment-group women were on the dole at some point between ages 26 and 40, compared with only 41 percent of the untreated.

They also clocked far more time on welfare—an average of 59 months—compared with 24 months for nontreatment females. More disappointing still were the findings related to children of the Perry participants. As the report puts it: “The two oldest children raised by program-group members did not differ significantly from the two oldest children raised by no-program group members in education, employment, arrests, or welfare status.” In the debate over economic and cultural causes for poverty, the economic camp argues that if poor parents had higher earnings and savings, less material hardship, more residential stability, and less parental incarceration, their children would be more successful. The Perry data fail to support that theory.

As Hymowitz notes, this doesn't mean that the Perry experiment achieved nothing. In fact, if it could be replicated on a large scale and in a different workplace and cultural environment, it might even help reduce crime and the sum total of human suffering–marginally.

What it would not do, Hymowitz argues, is have a significant effect on inequality.