The state of New Jersey has been funding full-day pre-kindergarten in certain low-income school districts since 1998. So when New York City Mayor Bill de Blasio said he wanted to expand pre-k — and gave himself seven months to enroll 53,604 kids — it was natural to look across the river for pointers. 

One thing New Jersey educators told WNYC: the mayor's pace of expansion is ambitious. In the first year of universal pre-k, New Jersey enrolled fewer than 6,000 students. It took the state 15 years to get to its current enrollment: 45,000 preschoolers.

“I certainly want to be supportive of the mayor’s objective, but I will tell you based on our own experience here in the state, that we could not have ramped at that level,” said Chris Cerf, the outgoing education commissioner in New Jersey. “And we put our shoulder into this.”

Serving pre-k students costs New Jersey $650 million a year. 

“Given the immense, and I think appropriate, costs of doing this, you don’t want to define success by the number of kids you’re serving,” Cerf said. “You want to define success by the number of kids who are being served well.”

Getting all pre-k teachers certified took six years in New Jersey. And finding classroom space remains a challenge. Sandra Rodriguez heads the early childhood education program in Newark which serves 6,700 students and employs 462 teachers.

“We have two areas of the city that if I were to open up a preschool, I’d fill it by close of business,” Rodriguez said.

A spokesperson for de Blasio said the city would rely on hundreds of community-based organizations and schools already providing pre-k to "rapidly scale-up,” and offer more seats.  

This raised a red flag for Ellen Frede with Acelero Learning who helped implement New Jersey’s pre-k program. She said infusing community groups with a lot of money in a short period of time raises its own set of challenges.

In New Jersey, some of the community-based organizations misused funds. Others didn’t know how to keep their books. It turned out business skills and oversight were needed in addition to early childhood expertise.

But when it comes to the payoff of pre-k, there is little debate. A study by the National Institutes for Early Education Research found that the number of New Jersey students held back a grade went down by 8 percent when they attended one year of pre-school. Enrollment in special education also dropped.

And kindergarten teachers say they see the difference. Regina Wingo, who teaches at Mount Vernon Elementary School, said she can always tell which students didn’t attend pre-k.

“Their dialogue is less; they don’t speak a lot," she said. "They’re not used to the classroom setting."

New Jersey was supposed to expand pre-k to the entire state this school year. But the state didn’t fund it. Perhaps this is another lesson for de Blasio: he has argued against state funding in favor of a dedicated revenue stream — a tax on the city's wealthy residents — to pay for his program, so pre-k is not subject to political budget games.

Mount Vernon Elementary School Kindergarten class in Newark (Sarah Gonzalez/WNYC)