In a growing number of classrooms around the country, 4 is the new 5 and preschool the new kindergarten.

Hoping for a future payoff of better schools and sharper students, states are aggressively expanding publicly funded programs to the youngest students — 4 or even 3 years old.

And eschewing play-oriented daycare, states are setting new academic standards, including class sizes and teacher credentials, to provide higher quality education before the first day of kindergarten.

Led by states such as Florida, Maryland and North Carolina, enrollment in public pre-K by 4- and even 3-year-olds jumped 40 percent from 2001 to 2006.

Excluding federal Head Start programs for poor children, the pre-K landscape now spans 38 states and covers nearly 1 million children, according to the National Institute for Early Education Research at Rutgers University.

It's not only such short-term benefits that advocates of publicly funded pre-K are counting on. They point to studies that suggest students who spend significant time in pre-K are likelier than their peers to behave in school, graduate from high school and be productive citizens.

"A good pre-K program has a chance to change the climate in a lot of schools, to make schools safer places, to really reduce disruptive behavior in classrooms and benefit all children," said Steve Barnett, director of the Rutgers institute.

Skeptics agree preschool programs can have long-term benefits for low-income children who might not otherwise be exposed to enriching experiences found in more affluent homes. But they say proponents overstate the benefits. And they challenge the wisdom of devoting dollars for richer kids whose learning gains, they say, are not nearly so dramatic or long lasting.

"Quality preschool gives a lasting boost to children from poor families," said Bruce Fuller, director of the Policy Analysis for California Education, an independent policy research center based at University of California-Berkeley and Stanford University. "But middle-class children only benefit slightly and by fifth grade, the effects have washed out."

Academic arguments aside, many states view preschool as an attractive place to spend taxpayers' money. Several states, including Iowa, New York and Oklahoma, either offer schooling for most 4-year-olds or are in the process of doing so, Barnett said.

Nationally, public pre-K serves about 3 percent of all 3-year-olds and 30 percent of all 4-year-olds, slightly more than the number of children in Head Start, the federal program started 40 years ago for the country's poorest children, according to the institute.

Though offered at some level in many states, pre-K attendance is not mandatory. All but eight states, in fact, do not require children to attend school until age 6, according to the Education Commission of the States.

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