President Obama’s call for universal preschool in his State of the Union address underlines a national shift in thinking about early childhood education, driven by advances in neuroscience and a growing urgency about the need to close the achievement gap between poor and privileged children.

A small but increasing number of states have invested tax dollars in preschool during the past decade, and millions of parents are walking their 3- and 4-year-old children into classrooms instead of keeping them at home or with a babysitter.

Much of this new emphasis stems from research about the developing brains of young children.

“People learn more in the first five years of life than they do in any other five-year period,” said Andrew Meltzoff, co-director of the Institute for Learning and Brain Sciences at the University of Washington.

“Kids are just like little sponges in the first 2,000 days,” of life, said Meltzoff, who believes researchers are on the edge of profound new discoveries regarding early learning. “They’re engaged in very avid and rapid learning in ages 3 to 5 . . . They’re tuned into the physical world and how the world works, and they’re also tuned into the social world.”

In his Tuesday night address, Obama proposed working with states to make high-quality preschool available to every child in America, saying that such education pays huge dividends by boosting graduation rates, reducing teen pregnancy and bringing down violent crime.

“In states that make it a priority to educate our youngest children, like Georgia or Oklahoma, studies show students grow up more likely to read and do math at grade level, graduate high school, hold a job and form more stable families of their own,” Obama said. “We know this works. So let’s do what works and make sure none of our children start the race of life already behind. Let’s give our kids that chance.”

The president made no mention of how much it would cost to provide universal preschool or how it would be funded.

The Obama administration focused much of its first-term education agenda on K-12 school reform and college affordability. In 2011, it spent a relatively small amount of money, $633 million, on competitive grants for states to create high-quality preschool programs. Thirty-seven states applied for the four-year grants; nine won the funding.

Educators see high-quality early childhood education as especially important to help close the achievement gap, which has been demonstrated to exist among children as young as 3 years old.

By age 3, children of white-collar parents have a working vocabulary of 1,116 words, while children in working-class families know 749 words and children whose families are on welfare know 525 words, according to an oft-cited 2003 study by Betty Hart and Todd R. Risley.

Several studies suggest that preschool is particularly valuable for low-income children. These children are less likely to end up in the criminal justice system, more likely to be employed and earn higher incomes, and less likely to receive public benefits as adults, when compared to at-risk children who do not attend preschool.

“The way you measure the benefits are not necessarily in grades or better test scores, but really those kids seem to do better as adults,” said Tracy King, a pediatrician who teaches at Johns Hopkins University Medical School.

Early education for low-income children is estimated to generate $4 to $11 in benefits for every dollar spent on the program, according to a cost-benefit analysis funded by the National Institutes of Health. Nobel Laureate James Heckman, an economist at the University of Chicago, says the return on investment for preK is stronger than the stock market’s average performance since World War II.

The potential benefits of preschool has led nine states and the District to fund free preschool for all 4-year-olds, growing from just three states a decade ago. The District also offers free preschool for 3-year-olds.

The percentage of 4-year-olds enrolled in state-funded pre-K programs doubled from 2000 to 2010, while the percentage of 3-year-olds increased slightly. The recession slowed or halted growth of programs in many states. 

Nearly half of all 4-year-olds and 20 percent of 3-year-olds were enrolled in state-funded or federally funded preschool programs in 2011, according to the National Institute for Early Education Research at Rutgers University. Those state-funded programs cost taxpayers about $5.5 billion, an average of about $5,000 per child.

Including private preschool enrollment, up to 75 percent of all 4-year-olds and 50 percent of 3-year-olds nationwide were in classrooms during the 2010-2011 school year, the institute estimates.

Still, 10 states do not fund preschool of any kind. Several, including Indiana, do not compel children to attend kindergarten, so some children have their first school experience in first grade at ages 6 or 7.

Critics of an expanded government role in preschool say the country has plenty of experience with federal preschool education — the Head Start program — and the results are lackluster.

“Overall, there is very little evidence of lasting benefits from Head Start,” said Andrew J. Coulson of the Cato Institute, a conservative think tank. “We’ve had Head Start for 50 years, and we still have an achievement gap. On the whole, the program doesn’t seem to have accomplished what it set out to accomplish.”

Head Start, created in 1965 as part of President Lyndon B. Johnson’s War on Poverty, is designed for 3- to 5-year-old children from low-income families. Head Start services vary by location, but they include medical care, meals, social services and education. The federal government runs another program, Early Head Start, that provides similar services for pregnant women and children up to age 3.

Last year, federal officials released a study of Head Start that found for most children in the program, academic benefits faded by third grade. There was one exception: Children from at-risk families who enrolled at age 3 showed sustained academic gains through third grade.

The Obama administration has begun cracking down on ineffective Head Start providers, notifying 254 of the 1,600 providers that they were “deficient” in terms of quality and would have to compete for funding, instead of getting automatic renewals.

In the Washington region, there’s a wide range in publicly funded early childhood education. In wealthy Loudoun County, about 1,000 low-income, at-risk and special education children are enrolled in preschool. Far more students start school with half-day kindergarten at age 5. In the District, which has a much higher poverty rate, about 13,000 children are enrolled in full-day, publicly funded preschool, open to any 3- and 4-year-olds.

“What D.C. is doing with 3-year-olds is incredibly atypical relative to the rest of the country,” said Daphna Bassok, an assistant professor at the Curry School of Education at the University of Virginia.

D.C.’s preschool program, which operates through a lottery system, costs taxpayers $122 million annually, according to the National Institute for Early Education Research. 

When Ivette Basterrechea, a lawyer and consultant who lives in Anacostia, won a space in the lottery for her 3-year-old daughter several years ago, she didn’t hesitate.

“The big motivation was not so much because we thought preschool education was so great in D.C., but we wanted to get out of day care so we wouldn’t have to pay,” she said. “I don’t think I’m alone in that.” 

Yet for 4-year-olds, “I don’t know why anyone would not want to send their child to preK,” she said. “It’s not a choice. It’s hugely beneficial.”

The Center for American Progress, a left-leaning think tank, is calling for universal access to preschool for 3- and 4-year-olds, with costs shared between the federal and state governments. For infants up to age 3, the center wants an expansion of federal child care subsidies and a doubling of Early Head Start programs.

That plan would initially cost $98.4 billion for preschool, $84.2 billion for child-care subsidies and $11.5 billion for Early Head Start, spread over about 10 years. The programs would cost about $25 billion a year to operate.

Neera Tanden, the center’s president, said investment in early childhood education amounts to “pennies” compared to the rest of the federal budget. She called it crucial to the country’s longterm economic health.

“China and India are investing tremendous amounts in the pre-school years,” she said. “We live in a global competition where people are looking for the best workers. This is about insuring that kids don’t fall behind before they even enter the race.”

Policymakers and education advocates caution that the quality of preschool in the United States varies wildly, creating uneven results.

“The challenge we have is how do we ramp those up in intensity and ramp up support for teachers and for kids in these programs,” said Robert C. Pianta, the dean of the Curry School of Education at the University of Virginia. “What we don’t need is another level of bureaucracy these programs need to deal with.”