By the time they start kindergarten, many children are already 18 months behind.
That - along with studies showing that money invested when kids are 3 or 4 years old helps them graduate or keeps them out of jail - is one reason states are starting to take a much harder look at funding education before they get to kindergarten.
Last month, Illinois Gov. Rod Blagojevich (D) proposed an initiative that would make the state the first in the US to offer universal preschool to 3-year-olds.
In June, Californians will vote on a ballot initiative to provide prekindergarten to all children. Legislators and governors are talking about universal preschool in Virginia, Arizona, New Jersey, and other states. And last year, at least 26 states increased spending on their preschool programs.
"If you look at pre-K as a national movement, it's continuing to move across the country, and we think California is indicative of that," says Don Owens, a spokesperson for Pre-K Now, an early childhood- education advocacy group.
But even as proponents tout the idea as the only safe educational investment, some critics question lavishing money on toddlers. They cite the "fadeout" effect some studies have shown, in which educational gains disappear after a year or two, and question the wisdom in offering universal pre-K, rather than targeting high-quality programs to children who need it most.
"I think [Illinois] is already doing a decent job with the really high-needs kids," says Collin Hitt, an associate with the Illinois Policy Institute, which advocates small government.
Mr. Hitt cites the Head Start studies that have shown limited gains for youngsters enrolled in the program, and studies from Georgia - one of three states, along with Oklahoma and Florida that currently has a universal pre-K program - that show any educational gains disappear within a year or two.
But some studies show significant long-term effects, not all academic. The High/Scope Perry Preschool Study spent more than 40 years tracking 123 African-Americans who went through a preschool program in Ypsilanti, Mich., comparing them with a control group. Those with preschool were more likely to graduate from high school and about half as likely to need special education. About four times as many owned their own home by age 27 and were earning at least $2,000 a month. They were less likely to be arrested, be on welfare, or have a child out of wedlock.
"Even though since they're way in the future, you discount them, those benefits outweigh the costs under pretty much any scenario you can think of," says Clive Belfield, an economics professor at Queens College at the City University of New York. The return can be as high as $12 for $1 invested, he says, although it's lower - $1.50 to $3 - for his analyses of universal state programs.
Currently, states' commitment to preschool varies: 41 states have some sort of pre-K program, but some serve only 1 or 2 percent of their state's 4-year-olds. Some require bachelor's degrees for teachers, and have different teacher pay scales. And some states have strict class-size limits while others, like Texas, have no limits.
But quality teachers and strong supervision can make a huge difference. "We have strong evidence that programs that have these characteristics are highly effective," says Steven Barnett, director of the National Institute for Early Education Research (NIERR). "But then people go and do research on stuff that's not like that and say, 'see, it doesn't work,' " he adds.
Florida has been criticized for cutting corners on quality, and Georgia doesn't require bachelor degrees for its teachers, but Oklahoma has won high marks from everyone. About two-thirds of all 4-year-olds are enrolled in the state - considered about the upper limit in universal programs, which are always voluntary.
"It is producing very impressive short- term learning gains for children," says William Gormley, a public policy professor at Georgetown University. "And it produces benefits for both disadvantaged children and middle class children."
Illinois - which already scores a 9 out of 10 on the NIERR's quality ranking - is hoping to reach some of those middle-class children who often don't qualify for targeted programs but whose parents can't afford private preschool.
"This is some of the most effective spending the government does," says Elliot Regenstein, the governor's director of education reform. Within five years, he says, Illinois hopes to have half-day preschool programs - up to the state's current high-quality standards - available to all 3- and 4-year-olds whose parents want it.
Others suggest a slow increase, but agree that two years is a good goal. "We believe a state should serve as many of its 4-year-olds first and then move to its 3s," says Mr. Owens of Pre-K Now. "But if the Illinois plan passes, Illinois will be the leader in the nation on prekindergarten."