Lessons for de Blasio in New Jersey's Free Pre-K Heidi Kottas works with Teddy Lin, 3, center, and Adrian Figueroa, 4, in Union City, N.J. Suzanne DeChillo/The New York Times UNION CITY, N.J. - Teddy Lin's teachers were worried. For the first few weeks of preschool, Teddy, a 3-year-old Chinese immigrant, cried nearly every day. While his classmates recited stories in English about dogs and elephants, he talked in Mandarin. Some days, he sat quietly and refused to play. His teachers responded with a radical plan. They began learning Mandarin, tutored his parents in reading, and paired Teddy with older classmates to teach him about topics like woodland animals. Within a few months, Teddy was performing on a par with his peers. Officials across the country, including Mayor Bill de Blasio of New York, are looking to efforts like those in New Jersey as they seek to broaden access to free, full-day prekindergarten. President Obama embraced the policy last year, and politicians in several states, including Maryland, Texas and Washington, are considering ambitious expansions. Though experts differ on the long-term benefits of preschool, the programs in 31 low-income districts in New Jersey are widely acknowledged for strong results. But they are also more expensive and intensive than what many officials - including Mr. de Blasio and Gov. Andrew M. Cuomo of New York - have proposed. In New Jersey, students attend prekindergarten for two years, not one. Class sizes are limited to 15. Teachers generally have more training than in New York. And it took more than a decade to perfect the model: The districts faced a host of challenges, including persuading families to enroll and rolling out a robust curriculum. A top priority of Mr. de Blasio is persuading state lawmakers and the governor to pass a tax on high-income city residents to pay for universal prekindergarten, and on Monday he is expected to present his case in Albany. But New Jersey's example suggests that even if he is successful, he will face perhaps a greater challenge: making prekindergarten programs worth the money. "We have to get this right," said Geoffrey Canada, the leader of the Harlem Children's Zone, which operates prekindergarten and charter schools. We do not need another lousy service for poor kids that we feel good about but that doesn't actually accomplish anything. During his campaign for mayor, Mr. de Blasio presented his prekindergarten plan as a way of reducing inequality in the city. He pointed to persistent disparities between poor children and their more affluent counterparts, noting research that shows language gaps emerge in children as early as 18 months. Scholars have long debated the best way to address those inequities. Studies of two landmark programs, the Perry Preschool Project in Michigan and the Abecedarian Project in North Carolina, suggested the answer might rest in early childhood education. Students who participated in the programs showed some academic improvement and were more likely to avoid negative outcomes later on, such as arrest and teenage pregnancy. But some education experts have cast doubt on the relevance of those studies, given that they involved small groups of students and took place several decades ago. And they have warned that prekindergarten is not a panacea, noting a 2010 study that showed some of the benefits of the federal Head Start program had faded by the end of first grade. "We know a lot less about what works in early childhood programs than the prevailing policy narrative would suggest," said Grover J. Whitehurst, a fellow at the Brookings Institution and a former federal education official. He suggested that rather than offering prekindergarten to all 4-year-olds, New York should focus its efforts on low-income children, who have been shown in studies to make larger gains than their counterparts. Such a program might not be politically palatable in New York, where preschool classes in middle-class neighborhoods often have long waiting lists. Mr. de Blasio has rejected the idea of limiting enrollment to poor students. "It is for everyone," he said last year. Doesn't matter if you're wealthy, doesn't matter if you're poor, doesn't matter what color you are, what neighborhood you live in. New Jersey began offering universal prekindergarten in 31 of its poorest school districts, including Union City, after a court ruling in 1998 demanded more funding for early education. Union City serves about 1,900 prekindergarten students, many of them the children of Latin American immigrants. One recent day, Teddy and his classmates matched objects - footballs, sleighs, flowers - with the names of the seasons. "At this age, they are sponges," said Lucas Abreu, a physical education teacher. People might think this is glorified day care, but it's the opposite. They learn to be students. They come out of their shells. A number of the New Jersey districts had difficulty recruiting students at first and resorted to creative marketing. They lined trays at McDonald's with fliers, hit the Sunday speaking circuit at churches, and hung bilingual banners emphasizing that the program was free. "There was a cultural shift," said Stanley M. Sanger, the Union City schools superintendent. Education officials here estimate that they now enroll virtually all of the city's 3- and 4-year-olds in preschool programs for six hours each day. Some students participate in a summer program as well. New York City has long provided preschool opportunities to children - it educates about 58,000 4-year-olds, most of them black and Hispanic. About two-thirds of those children attend part-day programs, which last two and a half hours each day, compared with six hours and 20 minutes for full-day programs. Mr. de Blasio's plan calls for expanding access to full-day prekindergarten to 48,000 more in the next five years. The number of low-income families in the city who choose to enroll their children in prekindergarten is still disproportionately low. About 52 percent of prekindergarten students qualified last year for free or reduced lunch programs, city data shows; across the city, 75 percent of students qualify. New Jersey's experience with prekindergarten offers some evidence that two-year prekindergarten programs may be more valuable to disadvantaged students than one-year programs, as Mr. de Blasio has proposed. A Rutgers University study last year of prekindergarten programs in high-poverty New Jersey districts showed that students who participated in prekindergarten as 3- and 4-year-olds outperformed those who enrolled for only one year. Under Mr. de Blasio's plan, 3-year-olds would not be eligible. The mayor's advisers noted that several school districts, including Boston's, had shown promising results with only one year of preschool. New Jersey preschool teachers tend to have more training than those in New York. New Jersey requires all preschool teachers to have certification in early childhood education. In New York, teachers employed directly by the Education Department must hold similar credentials. But about two-thirds of all preschool programs in the city are run by community groups, where teachers need to show only an intention to become certified within five years; as a result, they are paid around $24,000 less than their counterparts in New Jersey. Mr. de Blasio has yet to offer specifics about teacher salaries or credentials. His proposal, based on revenue from the tax he is seeking, sets aside about $10,000 per student per year. In New Jersey, the cost is about $13,000. Mr. Cuomo's plan, which would use state funding but no new tax, appears to allot far less money for the city, though the governor recently signaled he would be willing to pay whatever costs Mr. de Blasio's program accrues. Wiley Norvell, a spokesman for the mayor, said that the quality of his prekindergarten programs would be "above and beyond what currently exists in New York City." "Quality and universality we see as equally important, and we are aggressively pursuing both," he said. One of Mr. de Blasio's most immediate challenges will be to find space to house new prekindergarten programs. Many schools are already strapped for classroom space, and some have reduced such programs in recent years to make room for an influx of kindergarten students. In Union City, space is less of a concern. In 2007, the school district opened a $13 million, 38,000-square-foot early childhood center, complete with a health center, kitchen and playground. Mr. de Blasio's plan sets aside $50 million each year to rent space; some possible sites include day-care centers, housing developments and libraries. Another option may be charter schools, which are lobbying for a change in state law so that they can offer prekindergarten classes. Mr. de Blasio has been critical of charter schools but recently suggested a willingness to work with them. Gail B. Nayowith, a member of a six-person task force appointed by Mr. de Blasio to carry out his prekindergarten plan, said that while the mayor wanted to ensure positive academic outcomes, that was not the only goal. With more children enrolled in prekindergarten, she said, parents would be able to work more hours during the day. "It's not just the implication for the 4-year-old, it's also what it means for the family," Ms. Nayowith said in an interview. If we want people to live, work and raise their children in New York, we have to be able to meet their needs. She was confident the city could hire enough teachers and find space to open thousands of seats by September. "It may not be pretty," she said, "but the doors will be open."