A new study by Johns Hopkins University's Center for Data-Driven Reform in Education casts more doubts on the commonly held belief that expanding state-funded preschool programs is a "can't miss" venture. This new report found that only three of 28 programs studied showed "strong evidence of effectiveness" once their participants finished kindergarten.

Ironically, earlier this week, Michigan's State Board of Education recommended adding taxpayer-funded universal preschool to our $20 billion public school system. To justify this, the Board claimed that economists say every $1 spent on early education programs would return $3 worth of benefits.

Similar claims are made by advocates for many other government spending proposals. In this instance there is in fact no consensus among economists that spending more on early childhood education pays dividends. Those who advocate it base their claims on extrapolating to the entire population the results of programs like the High/Scope Perry Preschool and Carolina Abecedarian Project. This is problematic for a number of reasons.

First, studies of these programs' results are limited and none match the methodological standards used in the Johns Hopkins report cited above. Also, these programs costs much more than current tax-funded programs, like Great Start and Head Start. The Abecedarian project cost between $11,000 and $16,000 per child and the High/Scope Perry Preschool cost about $12,000 per child.

Finally, these projects involve far more than just an extra year of schooling, including tutoring beyond preschool, home visits, parental counseling and initial interventions beginning as early as infancy. Extrapolations that assume equally intense engagement in a much larger population are not realistic.

Recognizing the dearth of evidence on the long-term effects of tax-funded preschool programs, the recent Johns Hopkins study calls for more longitudinal studies that meet social science standards.

Perhaps the best example is one released just a few months ago by the U.S. Department of Health and Human Services. Similar to the Johns Hopkins study, it found that by the end of first grade, Head Start participants could not demonstrate any statistically significant beneficial gains when compared to a randomized control group of non-participants.

In light of such evidence, the public should be highly skeptical of this latest call from the status quo public education establishment for an expensive, state-run, taxpayer-funded universal preschool project.