“I'll gladly pay you Tuesday for a hamburger today.” That line helped the infamous Popeye cartoon character J. Wellington Wimpy pack on the pounds year after year. Government-run preschool boosters have been making similar promises for decades. Yet students and taxpayers are still waiting for their payday Tuesday.

Government preschool enthusiast Nicholas Kristof of The New York Times admits as much in a recent column, noting that “early education has always had an impact not through cognitive gains but through long-term improvements in life outcomes.”

Those of us not deluded by Nilla Wafer wishes and juice box dreams are probably wondering how a better life is possible without cognitive improvement.

Frankly, it isn’t—and that’s a big problem for high-profile backers of universal government-run preschool.

President Obama’s $100 billion Preschool for All initiative took center stage of his 2013 State of the Union. Democratic House Leader Nancy Pelosi also made universal preschool a top priority in her Economic Agenda for Women and Families released last summer.

For all the publicity, the pricey plans went nowhere fast in Congress. Scaled-back funding did make its way into the omnibus spending bill passed last month, including some $250 million for states to expand preschool through the Race to the Top Early Learning Challenge, along with an additional $600 million for the country’s longest-running preschool program Head Start.

But those amounts were a far cry from the billions upon billions of dollars preschool supporters were hoping for.

One reason is that government-run preschool impacts quickly fade out once students enter elementary school according to official evaluations by the U.S. Department of Health and Human Services. Touted localized programs are also suspect in terms of real results.

Claimed impacts from the small-scale Perry Preschool and Abecedarian preschool programs from the 1960s and 1970s have never been replicated—a real red flag for policymakers looking for model programs. A subsequent federally supported program in Chicago during the 1980s offered in-home care, tutoring, and parent classes for low-income, at-risk participants—hardly a run-of-the-mill “preschool” program.

But what about other studies by Harvard and UCLA researchers cited by Kristof purportedly showing positive long-term outcomes for Head Start participants? Both studies note the well documented phenomenon of fade out. Yet researchers can only estimate the likelihood of better outcomes on participants because only short-term evaluations are conducted—even though Head Start began in 1965.

None of this has stopped Obama, Pelosi, Kristof, and others from linking any number of long-term benefits to government preschool, from more than 10 to 1 rates of return on taxpayer subsidized “investment,” to reduced incarceration rates, and higher college attendance rates.

In the real world, private investors demand proofs of concept before they invest their hard-earned dollars. We should hold government to the same standard with any program it seeks to implement or expand—especially when those programs affect children.

Kristof is right that preschool will be one of the top public policies issues this year. But he’s wrong that those of us who question the results are off base and need schooling.

It’s high time for the J. Wellington Wimpies of this world to make good on their promises of preschool-driven excellence to generations of children and taxpayers—now, not decades worth of Tuesday’s from now.