NEW YORK -- When Neil J. McNeill Jr., principal of the Middle School for Art and Philosophy in the borough of Brooklyn, learned that fewer than 4 percent of his students had passed state exams in math last year, he was frustrated.

It so happened that he shared a building with one of the top-performing schools in the Brownsville neighborhood, Kings Collegiate Charter School, where 37 percent of the students had passed, well above the New York City middle-school average of 27 percent.

Mr. McNeill had long been curious about the charter school's strategies: It, too, served large numbers of low-income black students, many from the same neighborhoods. But the two schools operated in their own bubbles, with separate public-address systems and different textbooks. And as a matter of practice, they did not talk about academics.

"We are kind of two ships in the night," Mr. McNeill, 39, said recently.

A primary rationale for the creation of charter schools, which are publicly financed and privately run, was to develop test kitchens for practices that could be exported into the traditional schools. President Barack Obama, in recently proclaiming "National Charter Schools Week," said they "can provide effective approaches for the broader public education system."

But two decades since they began to appear, educators from both systems concede that very little of what has worked for charter schools has found its way into regular classrooms.

Testy political battles over space and money, including one that became glaringly public in New York state this spring, have inhibited attempts at collaboration. The sharing of school buildings, which in theory should foster communication, has more frequently led to conflict. And some charter schools have veered so sharply from the traditional model -- with longer school years, armies of nonunion workers and flashy enrichment opportunities like trips to the Galapagos Islands -- that their ideas are viewed as unworkable in regular schools.

In recent years, educational leaders, concerned about hostilities between the two types of schools, have worked to foster warmer relations. In Tulsa, Okla., charter schools and district schools are working together to improve teaching quality. And in Spring Branch, Texas, charter school leaders are helping train district teachers and principals.

The Bill and Melinda Gates Foundation has helped finance some of those efforts, offering $25 million in grants over the past several years for educators interested in tackling common problems.

Education experts said it might prove difficult to encourage the kind of sharing of ideas that charter schools were originally supposed to foster, given competitive dynamics. Charter schools serve about 5 percent of students nationwide, according to the National Alliance for Public Charter Schools, up from about 1 percent in 2003. In some cities, like Detroit, New Orleans and Washington, the percentages are much higher. (In New York, it is 6 percent.)

"It's like putting a Burger King kitty-corner to a McDonald's and expecting -- in the same location and competing for the same families -- warm and fuzzy cooperation," said Bruce Fuller, a professor of education and public policy at the University of California, Berkeley.

Charter schools are known for aggressive recruiting campaigns, and at schools with dwindling enrollment, every student counts: In New York, each brings more than $10,000 in education financing.

The first charter schools in the United States opened in the early 1990s, and were popular among advocates interested in radically overhauling the traditional model of schooling. The schools were given freedom from regulations about staffing, curriculum and scheduling in hopes that they could devise superior models.

As their numbers grew rapidly over the past decade, tensions worsened in many cities. Labor groups have emerged as some of the most vehement critics of charter schools, which are typically not unionized, depriving them of members.

Charter school leaders have defended their efforts, pointing to strong academic results in some of the poorest neighborhoods. But some also acknowledge that the tactics of the movement were partly to blame for the reluctance of district leaders to work with them.