Shikha Dalmia and Lisa Snell write

The only preschool programs that seem to do more good than harm are very intense interventions targeted toward severely disadvantaged kids. A 1960s program in Ypsilanti, Mich., a 1970s program in Chapel Hill, N.C., and a 1980s program in Chicago, Ill., all report a net positive effect on adult crime, earnings, wealth and welfare dependence for participants. But the kids in the Michigan program had low IQs and all came from very poor families, often with parents who were drug addicts and neglectful.

Even so, the economic gains of these programs are grossly exaggerated. For instance, Prof. Heckman calculated that the Michigan program produced a 16-cent return on every dollar spent — not even remotely close to the $10 return that [its] advocates bandy about.

“Universal pre-school” is a cause that appears to be enjoying growing popularity among those who don’t think that government has enough on its plate already, or that it can ever have enough on its plate.

Dalmia and Snell want to engage the LFs on what the research shows. That will not work. When you know that the state rather than parents ought to be raising kids, evidence is not going to make a difference.