"Life Is Good" sign on the wall in the main office of PS 149 in Harlem, New York. (Photo by Thomas Prior for MSNBC)

MSNBC —The dramatic rise of charter schools in urban communities over the past decade has been fraught with debate, controversy and consternation. Opponents of charters, which are publicly funded but operated by private groups, say the schools have been used as a tool to break unions and privatize public education. Those critics say that with each new charter school, desperately needed funding is being redirected from traditional public schools that have been starved for resources for decades.

While the broader debate over charter schools is whipping through communities across the nation, the epicenter remains in New York City — specifically Harlem — where a plethora of charters have emerged to challenge public schools for students and the funding that follows each of them. They’ve grown in neighborhoods with high concentrations of poverty and need, where many local schools have long failed to offer students a quality education.

Indeed, New York City has bucked a national trend in which charter schools in major cities throughout the country have typically not performed any better than their traditional public school counterparts, and in many cases have performed much worse.

In Harlem, the success and aggressive expansion of charter schools has created a toxic dynamic as traditional schools languish. Over the past decade, as dozens of public schools were being shuttered in New York City, charter schools grew more than tenfold. The city’s charter schools were favored by former Mayor Michael Bloomberg, as well as wealthy Wall Street donors who have poured millions in cash and resources into them. Under Bloomberg’s administration, the number of city charters grew from just 12 when he took office to 183 a dozen years later.

But there’s one Bloomberg-era policy in particular that has served as a lightning rod in the city’s charter school debate. It’s called co-location, and it allows charter schools to occupy rent-free space in public school buildings. The result is a complicated cohabitation in which school buildings are literally dissected by multiple schools, students and administrations.

Critics say the policy of co-location has created a two-tier system of haves and have-nots, where students at traditional public schools are losing valuable space and programming while charters enjoy the spoils of public funding in addition to wealthy private benefactors.

The most maligned — and academically successful — charter school network is the Harlem Success Academy, which operates 22 schools across the city.

Critics of Harlem Success say the schools have bullied their way into city-owned buildings and created what amounts to an apartheid system. The Success Academies typically renovate their spaces beautifully, painting the walls and gutting the bathrooms. They replace the lighting in their sections of public school buildings and carpet their classrooms. They have rooms for playing chess, dance studios, and rooms for children’s building blocks.

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