If one listens to Rob Reiner and his allies, universal preschool is an education silver bullet. Waving around a recent RAND report that claims that every tax dollar invested in preschool will generate up to $4 in a variety of societal benefits, Reiner is pushing an initiative that will provide government-paid preschool to all families, regardless of income level. The case for universal preschool, however, is much more porous than Reiner would have Californians believe.

First, RAND cites a number of studies that show preschool helps raise the achievement of low-income, mostly minority children and prevents problems such as crime and child abuse. Some of these studies, however, are of limited value due to tiny sample sizes — as few as 65 children. A recent policy brief put out by Princeton University and the Brookings Institution commented that studies with such small sample sizes make it questionable whether large-scale programs, like a universal statewide program, could attain similar success.

Another study used extensively by RAND compared 1,000 low-income minority children who went through a Chicago preschool program with 550 children who did not. The students in the study, though, were not randomly assigned to the experimental group, which went to preschool, and the control group, which did not. Thus, other factors could have affected the results.

RAND also cites the federal Head Start program, a long-running government preschool program for disadvantaged children. RAND admits that the program has had mixed results. In fact, a Health and Human Services department study found that any gains made by Head Start children diminished or disappeared once children entered regular school.

There is even more uncertainty about preschool's long-term effect on children from higher-income families.

In fact, the RAND report, which was funded by the pro-universal-preschool Packard Foundation, could only identify one study that looked at the longer-term benefits to more-advantaged children. RAND acknowledges, "This study found that children participating in preschools not targeted to disadvantaged children were no better off in terms of high school or college completion, earnings or criminal justice system involvement than those not going to any preschool." Yale professor Ed Ziglar, co-founder of Head Start, says that significant evidence shows that "there is little if anything to be gained by exposing middle-class children to early education."

Further, the evidence from Georgia, one of only two states with a statewide preschool, is not encouraging. In 2003, Georgia State University researchers found that after tracking students for five years, any test score gains from preschool "are not sustained in later years."

RAND and other preschool boosters point to France, which has a universal pre-kindergarten program. Yet the truth is that U.S. fourth-graders outscore their French counterparts in international reading tests. Only in later grades do U.S. students fall behind their foreign peers, which indicates that the U.S. problem isn't lack of preschool, but lack of quality education in post-elementary grades.

One of Reiner's selling points for his initiative is that it would require all preschool teachers to have a bachelor's degree and a teaching credential. However, even RAND admits that there are no scientifically sound studies comparing preschool programs that employ teachers with these qualifications and programs that do not.

With weak evidence supporting universal preschool, RAND resorts to the claim that political support may be "stronger for programs available to all children." In other words, higher-income families would back government-subsidized preschool as long as their children were getting subsidies, too.

Preschool for all is a seductive proposition, but the reality is that the purported benefits would likely be much less than what Reiner and his cohorts are promising. And with experts arguing that Reiner's cost estimate of $2 billion is way too low, universal preschool looks to be a very expensive bad idea.