Harlem — The state legislature's eleventh-hour vote last month to expand New York's charter schools will add 114 new charters to the 99 currently operating in New York City. But while the new law paves the way for new schools, and perhaps for millions in federal education funding, it doesn't create new space for the new schools—or for the current charters, which are bursting at the seams as they add students, year by year.

When a new school opens, it generally begins with one or two grades – typically, kindergarten and first – and "grows up the grades" over time, adding a new kindergarten cohort every year, as older children progress. This means that schools that aim to encompass K-8 begin small and eventually expand to a much greater size.

City Department of Education (DOE) officials say that 62,500 students will attend charter schools this fall. But rough estimates by the New York City Charter School Center suggest that about 140,000 students may eventually attend charter schools in New York City, once all of the charters reach capacity. Besides the 99 now running and the 114 authorized by the new state law, another 37 are already slated to open in the city in the next two years.

About two-thirds of New York City's charter schools are "co-located"—sharing space in public-school buildings. Comparatively scarce real estate and high rental and leasing costs necessitate building shares, according to the DOE's Jack Zarin-Rosenfeld, who notes that public schools have long shared building facilities in neighborhoods like the Upper West Side and brownstone Brooklyn, and adds that only 6 percent of students in co-located public schools attend charters.

Elsewhere in New York, and across the United States, charters have their own buildings, separate from traditional public schools. "Not every charter experiences a positive relationship with the school district," says Cynthia Proctor of SUNY's Charter School Institute, a reference to Chancellor Joel Klein's robust support for charters. In New York City, school leaders who apply to form new charters must submit plans for private space. But "the Chancellor has made it a priority to secure facilities for charter schools," according to the DOE.

How is sharing faring?

Some advocates for both traditional public and charter schools (which are publicly funded) say that co-locating charters in public-school buildings creates a two-tier school system–and fuels a destructive competition between parents for scarce resources.

"Co-locations were the most contentious issue in amending the charter law," said Mona Davids, head of the New York Charter Parents Association, whose daughter attends a charter middle school in the Bronx that's sited in a public elementary school building. Battles over space and resources fracture already-fragile communities, she adds. "This is pitting parents of color against each other. We are all public school parents." Davids says. "Co-location does not work. Charters should have their own buildings."

DOE decides whether to co-locate a charter by evaluating the charter application and assessing need, building capacity and available resources. Some school organizers have access to private space within their target community, and no need for co-location. Others may design a proposal for one neighborhood and have to choose between a DOE co-location offer in another part of New York or finding private space on their own. Co-location recommendations by the DOE are approved by the Panel for Education Policy, at the end of the school-approval process, and cannot be appealed.