Samantha Belmontes, 7, a student at Ricardo Flores Magon Academy in Denver, and classmates test their hand-eye coordination. Charters such as Magon Academy are public schools granted autonomy from some state rules. (Helen H. Richardson, The Denver Post)

Nearly 20 years after the country's first public charter school opened, charter schools in Colorado are enrolling more students than ever.

This year, charter schools nationwide logged their largest enrollment increase, with a population of more than 2 million students — including about 82,206 in Colorado — according to data released Wednesday by the National Alliance for Public Charter Schools.

"I think charters have become part of the mainstream of America's public education system," said Ursula Wright, the alliance's interim president and chief executive. "Though it's certainly a small percentage, at 5 percent of the total student population in 20 years, no one can continue to think of us as a marginalized phenomenon."

Charter schools are free, public schools operated by an independent board. They can be granted autonomy from various state laws, most commonly around hiring and firing practices.

Charters are also free to offer different curricula and services than traditional public schools.

Colorado's charter-school enrollment increased this year by 8,500 students, or 11.9 percent, ranking the state eighth in the country. The state also added 13 new charter schools.

California, the top state in the country for charter student growth, had an increase of about 47,000 students.

"I believe it's twofold," Wright said. "It's an increased public understanding of charters that has increased demand but also a stronger, more favorable environment that has been a benefit."

Among the 13 new Colorado charter schools, four are in Denver Public Schools, and two each in Douglas County and the Adams 12 school district.

Nationwide, more than 500 new charter schools opened, concentrated in a few states where recently enacted laws eased new charter-school creation.

In Colorado, the environment has been good and the demand high, said Jim Griffin, president of the Colorado League of Charter Schools.

"The demand has been there since the beginning," Griffin said. "What you continue to see is building and increasing political support for charters. We have all gotten collectively smarter about how to deal with barriers."

According to data from the Colorado Department of Education, the enrollment jump may be the second-largest for Colorado.

In 2009, charter-school enrollment increased by 8,713 pupils to 66,556, up from 57,843 in 2008.

The data archived online goes as far back as 1995, when Colorado had 22 charter schools and 4,107 students enrolled.

Overall student achievement at charter schools has been mixed, but recently, charter schools have been at the top of the best-performing public schools in the state.

Wright said autonomy helps charters succeed, but it's not the only factor for success.

"We don't have a target for charter schools that we're reaching for at all, because it's about reaching unprecedented levels of high academic achievement," Wright said. "Sometimes it will mean charter schools, or sometimes it will mean traditional schools adopting certain elements of autonomy or flexibility."

The National Alliance for Public Charter Schools report noted that about 150 charter schools were closed this year nationwide.

Since 1997, 26 Colorado charters have closed.

"There's always going to be a mix. Some will do well; some won't. We absolutely know that," Griffin said. "When charters get the right combination of people, program and leadership, they can do really well. That's not something we can say for centrally managed school districts."

Yesenia Robles: 303-954-1372 oryrobles@denverpost.com