Greg Toppo, USA TODAY
BROOKLYN, N.Y. - As taped piano music plays, Ashley Brown issues a stream of commands. Firm and insistent, she strides around the tiny studio and puts her third-period ballet students through their steady, rhythmic paces.

What her eighth- and ninth-grade dancers may not notice is the larger ballet they're part of: the fraught, decades-old dance - one step forward, two steps back - of who goes to school where, and with whom.

They're doing nothing less than integrating a city.

Now in its fourth year, Brooklyn Prospect Charter School is one of a small but growing group of schools that actively seeks to fill its seats with students from different racial, ethnic and socioeconomic groups. Researchers say schools like it are getting a boost from urban middle-class parents who are quietly saying "No" to the typical suburban exodus once their kids reach kindergarten.

"Many of them express a deep attachment to the city," said University of Pennsylvania sociologist Annette Lareau. "They see the suburbs as sterile, as boring. They also see the suburbs as not a realistic preparation for their children for life."

These parents increasingly push local schools to accommodate them, a development that Lareau says is "good for cities and good for America."

Observers caution that the trend of white middle-class parents sticking with urban schools is still small and won't soon reverse the USA's decidedly mixed record on school integration since the 1954 U.S. Supreme Court Brown vs. Board of Education, which declared "separate but equal" schools unconstitutional.

At the moment, researchers say, the phenomenon seems limited to a handful of mostly East Coast cities: New York, Boston, Philadelphia and Washington. But it's also happening in New Orleans, Chicago, Denver and San Francisco.

"All we can say at this point is that this provides the best opportunity in a generation for us to integrate our urban schools," said Mike Petrilli, whose the new book The Diverse Schools Dilemma, appears in stores . Another, Jennifer Stillman'sGentrification and Schools: The Process of Integration When Whites Reverse Flight, appeared last August. A third book, MarketingSchools, Marketing Cities, by Temple University education researcher Maia Cucchiara, is due out this spring.

For activists who never gave up on the dream of integration, Petrilli said, the change is palpable. "For four decades now, the issue of urban schools has been one of predominantly poor and minority kids and how to serve them well," he said. "Suddenly we have this influx of middle-class kids."

In many ways, these families are asking schools to turn a full 180 degrees from how many have operated. While a few urban systems have pushed for integration through busing, open enrollment and magnet schools, many have simply settled on offering something better, no matter where students attend school. To skeptics of that approach, the new, homegrown push for integration shows that families want something different.

"True educational equity can only occur in socioeconomically diverse classrooms," said Josh Densen, a veteran educator now working to open a new school in post-Katrina New Orleans, where thousands of young, idealistic professionals are starting families but can't afford private-school tuition.

For Densen, the pull of diversity was personal. A one-time teacher at a KIPP school in Harlem, he moved to New Orleans in 2009 and began looking for a socioeconomically diverse school for his daughter, who was just starting kindergarten. He couldn't find one, and parents he talked to couldn't find one either.

The city has several KIPP schools, which target low-income, minority students and get kids' academic skills quickly up to par. Densen acknowledged that KIPP schools change kids' lives, "but I didn't think my daughter was going to have that same need." Next month he hopes to persuade the Orleans Parish School Board to approve his plan for a diverse charter school.

Stillman, another veteran New York City educator, studied parents' school choices while earning her Ph.D at Columbia University's Teachers College. She found that gentrifying public-school parents come in four distinct "waves" that quickly tip the racial and economic balance of schools. Once a critical mass of middle-class parents begins saying favorable things about the school, she found, "it can happen pretty fast."

How fast? Two or three years.

One look at Brooklyn Prospect's student body shows what four years can do. Started as a middle school, it has added a grade each year and just enrolled its first freshman class. It's both racially and economically diverse: Last year, about 40% of students qualified for free or reduced-price meals, a key indicator of poverty. While that's above the percentage at most middle-class schools, it pales in comparison to the typical charter school, where more than 90% of students are often low-income.

After three years sharing space with other schools, it now occupies a 1960s-era four-story building that once housed a Catholic school. The charter school signed a 30-year lease with the local parish that allowed eight nuns to remain on the property. All eight live on the fourth floor, making Brooklyn Prospect, in all likelihood, the only public school in the USA with a convent on its top floor.

Now so popular, the school routinely picks new students by lottery. The school can't recruit by racial preference - but it holds 40% of seats for low-income students. Those that don't gain entry through the special lottery for just low-income kids get another chance in a second lottery, open to all students. "Diversity is not easy," said Daniel Rubenstein, the school's founder and executive director. "It doesn't just happen."

It also requires schools like his to push harder than most to help at-risk students. Teachers keep regular office hours and accommodate different skill levels. "That's what great teachers can do and that's why we go and get great teachers," Rubenstein said.

Asked whether it's frustrating for advanced students to work side-by-side with their struggling peers, he countered: "How do you possibly teach kids about the world without having students sit side-by-side, who don't look like each other and don't think very differently? Isn't that the more important skill?"

Reflecting on the lessons of the Brown court decision, he said forcing people to go to school together is problematic, but that excellence can build diversity. "If you offer a program that is attractive to a lot of people, with a little bit of tinkering you can really accomplish what lots of ... places haven't been able to," he said.

"This could be a golden moment because we do have people wanting to be in the cities," said Temple's Maia Cucchiara. "But you have to handle a golden moment right. It could be a really fabulous thing."