The schools specialize in math, science or the arts. Some are Afro-centric, others are religious. They are publicly funded but operate independently of local schools boards and, often, teacher unions.
They all make up the growing charter school movement that the Obama administration would like to see flourish.
"The charter movement is absolutely one of the most profound changes in American education, bringing new options to underserved communities and introducing competition and innovation into the education system," Education Secretary Arne Duncan told attendees at the National Alliance for Public Charter Schools' annual conference last week.
But not everyone agrees that charter schools should play an integral role in education reform.
"You should have a reason for increasing charter schools, and I haven't seen any rationale for doing that except for, 'Let's do it,'" said Gerald Bracey, an associate at the High/Scope Educational Research Foundation.
With $100 billion in stimulus funding for education, including $4.35 billion in the competitive Race to the Top fund to improve education quality, Duncan has offered a stern warning to states: Embrace charters or risk losing stimulus dollars.
"States that don't have charter laws or put artificial caps on the growth of charter schools will jeopardize their applications under the Race to the Top fund," Duncan told reporters last month. "Simply put, they put themselves at a competitive disadvantage for the largest pool of discretionary dollars states have ever had access to."
Governors are heeding Duncan's warning. On Monday, Tennessee Gov. Phil Bredesen signed a measure that expands the eligibility requirements to attend charter schools. On Tuesday, Indiana Gov. Mitch Daniels signed into law a budget that does not limit the establishment of new charter schools.
"He's blackmailing states, saying you either have to have charters ... or lift the caps, or your stimulus money will be at risk. There's no evidence out there to justify it," Bracey said.
A recent report by Stanford University Center for Research on Education Outcomes found a wide variance in quality among charter schools and reported that many students in charter schools are not performing as well as students in traditional public schools.
Last week, Duncan called the report "a wake-up call, even if you dispute some of its conclusions." But Duncan's reaction shocked Bracey.
"There are numerous studies out there showing that charters, compared to public schools, don't do as well," Bracey said.
Citing the Stanford report, Duncan warned charter school management that low-performing charter schools are endangering the success of their own movement and must be turned around.
"The charter movement is putting itself at risk by allowing too many second-rate and even third-rate schools to continue to exist. Your goal should always be quality, not quantity," Duncan said.
When he was head of the Chicago public school system, Duncan helped open 70 charter schools, but he also closed down three for academic failure and mismanagement.
Duncan went on to challenge charter operators to improve accountability.
"There should be a high bar for charter approval and, in exchange for real and meaningful autonomy, there must be absolute accountability," he said, highlighting states such as Arizona, Florida, Minnesota, New Mexico, Ohio and Texas, where he said accountability is "minimal" and "unacceptable."
In 2008, 1.3 million students were enrolled in the 4,303 public charter schools operating in 40 states and Washington, D.C. -- roughly 3 percent of the amount in the nation's public schools.
The head of the nation's largest teachers union was pleased to hear Duncan's firm warnings to charters.
"They are no longer equating charters with innovation, and that was a big point for us," National Education Association president Dennis Van Roekel told ABC News Thursday. "There are a lot of charters that aren't innovative. There are a lot of public schools, non charters, that are innovative."
As the Obama administration calls for more charter schools, unions also may push for a larger role in the movement. Charter schools typically operate free from the rules inherent in union contracts and have been criticized by teachers in the past for draining resources from traditional public schools.
Last week in New York, the United Federation of Teachers and the American Federation of Teachers formalized a labor deal with Green Dot, a charter school operator, for a New York charter school in the Bronx.
"This contract can serve as a blueprint for giving charter school educators a voice, for bringing innovations to the classroom and for looking at new ways to improve labor-management relations in our schools," said AFT president Randi Weingarten.
Although the contract does not guarantee tenure to teachers, it promises that no teacher will be fired without "just cause," and it calls for a 14 percent increase in teachers' salaries above the city contract levels.
"Across the country, we are hearing from more and more educators who want the fairness and professionalism that comes with union membership and a collective bargaining agreement," said Weingarten, formerly president of the UFT.
Andrew Rotherham, co-founder and publisher of the Education Sector, a Washington, D.C., think tank, lauded those involved in the deal for making the tough decisions necessary to compromise.
"I think it's an important touchstone," he said.
But Rotherham warned that the union agreement reached with Green Dot may not apply across the board.
"I would be careful in overgeneralizing from it," he said. "Some of these other [high-performing] schools, they just aren't going to take the risk."
Duncan has underlined the involvement of unions in charters.
"Charters are not inherently anti-union," he said last week. "Albert Shanker, the legendary head of the American Federation of Teachers, was an early advocate. Many charters today are unionized. What distinguishes great charters is not the absence of a labor agreement but the presence of an education strategy built around common sense ideas: more time on task, aligned curricula, high parent involvement, great teacher support, and strong leadership."
But this may not be entirely true, Bracey noted, saying that while Shanker was an early advocate of charter schools and helped launch the movement in the late 1980s, he later jumped ship. By 1994, Shanker described charters as "a recipe for chaos."
Van Roekel predicted more union involvement in charters.
"All charters are public schools, and, depending on the state law, in some of them they are unionized," he said. "In some states they aren't allowed to. As that works through, I think you'll see more of it, not less of it."