MINNEAPOLIS -- In Kitty Taylor's third-grade classroom at Hiawatha Leadership Academy, the pace is quick.
When Taylor hands students a math quiz, they have two minutes to finish before a timer goes off and they have to turn in their papers. Then they must snap to attention and move to the next task. "One, two, three, eyes on me," Taylor calls. "One, two, eyes on you," her students respond.
That's a tiny fraction of a very long day for the south Minneapolis charter school's nearly 400 students in kindergarten through fourth grade. Similar scenes are repeated across the nation in the some 5,000 charter schools that serve 2 million students.
This week, charter school officials will gather in Minneapolis to share notes and discuss the progress of the national charter school movement, which marks its 20th anniversary this year. The first charter school in the country, City Academy in St. Paul, opened in 1992 and is still in operation today.
Leaders of the National Alliance of Public Charter Schools say they expect nearly 4,000 people to attend the conference, which runs Tuesday through Friday.
Despite their growth, the schools' effectiveness is still being debated.
A University of Minnesota study found that students at charter schools in the Twin Cities, for example, scored 7.5 percentage points lower on math testing and almost 4.5 points lower on reading tests than their counterparts at traditional schools. National studies have found similar results across the country.
In Minnesota, 40,000 students attend charter schools, or less than 5 percent of the state's total K-12 enrollment. Though relatively small, enrollment at charters has tripled in the last decade.
Charter schools are public schools, but they are freed from some of the regulations that guide traditional schools. They operate independently, and develop their own curriculum and focus.
Advocates for charter schools say they offer families a choice over failing district schools and are particularly helpful for minority and low-income families.
Most of the students at Hiawatha Leadership Academy are Latino and from low-income families. Students there are in school from 7:50 a.m. until almost 4:30 p.m. Combined with a longer school year, the children spend 40 percent more time in class than the students in district schools.
Eli Kramer, executive director of Hiawatha Academy, said that's key to the school's mission of preparing students for college.
"Rigorous academics and a very heavy on focus on developing character and the social and emotional skills that we believe students need to thrive in a higher education setting," he said.
According to state testing data, since the school opened in 2007, its students have essentially closed the gap between their reading and math scores and those of white students.
Kramer said Hiawatha Leadership Academy is living up to what was promised of charters when they began in Minnesota 20 years ago, but he acknowledges his school's success isn't characteristic of the entire charter movement.
"There's a huge range of quality of charter schools," he said. "There are some terrible charter schools. We have to be honest with ourselves about that."
Two decades of data show that Minnesota charter schools often underperform compared with traditional district schools, said Myron Orfield, a law professor and director of the University of Minnesota's Institute on Race and Poverty. He authored the study on Twin Cities charter schools.
"Charters have promised something better to kids that are desperate and their families that are desperate and they've given them something worse," he said. "They've tricked them. And they've tricked us. And it's a tragedy."
Orfield's research has also found that more than 40 charters have closed in the Twin Cities since the mid-1990s because of financial mismanagement.
He thinks charters that routinely underperform traditional schools should be closed. Some charter school advocates concede that the charter system needs to change.
Among them is Bill Wilson, a former St. Paul councilman and state human rights commissioner who started Higher Ground Academy in St. Paul 12 years ago. Today 700 students are enrolled in the K-12 charter, and most are the children of East African immigrants.
Wilson said low-performing charter schools that do not follow the best practices of high-performing schools will not be around for long.
"Either they will find that they're going to be successful and stay in business, or they're going to be unsuccessful and go out of business," he said.
Despite the debate over standards, charter advocates say they expect more growth in the future.
They're calling for closer collaboration with district schools, something they say would be good for the entire public education system.