The Wall Street Journal  reports on research casting doubt on the consensus that if we could just get more disadvantaged kids to pre-school they’d have a better chance of keeping up later.

The research covered finds no significant benefit to American kids in a number of states who’ve had pre-school over those who have not, after several years at school. In some respects they may be worse. Here’s the crunch:

"If anything, preschool may do lasting damage to many children. A 2005 analysis by researchers at Stanford University and the University of California, Berkeley, found that kindergartners with 15 or more hours of preschool every week were less motivated and more aggressive in class. Likewise, Canada’s C.D. Howe Institute found a higher incidence of anxiety, hyperactivity and poor social skills among kids in Quebec after universal preschool."

New Zealand’s critical task is to deal with the 20%+ tail who leave school functionally illiterate. The report may be slightly less depressing for them:

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.