For the 2013-14 school year, charter enrollment in LA Unified jumped 15 percent, giving the district a total of 139,174 charter students, which totals 21 percent of its student body. In 2005-06, the district had a total of 35,310 charter students, with increases coming each year since.

Although it has by far the most total charter students of any district in the nation, LA Unified is behind 33 other districts in regard to the percentage of students enrolled at charter schools, the report found.

Nationally, the report found that at least one in five students now attends a public charter school in 43 communities across the country, up from 32 last year, and that 12 urban communities now enroll at least 30 percent of their public school students in charter schools, a jump from seven urban communities last year.

Over the past five years, charter enrollment nationwide has grown by 70 percent, the report found.

“This is a remarkable increase in the number and percentage of students attending public charter schools nationwide, and that is a major success for the growth of the charter school movement,” Nina Rees, president and CEO of the National Alliance for Public Charter Schools, said in a press release. “We now have 11 more communities that enroll at least 20 percent of their overall student population in public charter schools.”

The topic of charter schools — which are schools that receive some public funding but operate independently — is one of the most polarizing in education.

While many of LA Unified’s charters have demonstrated increases in student achievement, critics say the success of charters comes at a cost to traditional public schools. Moody’s Investor Service recently concluded that the coming expansion of KIPP charter schools in LA Unified was a credit negative, as it will result in a loss of $35 million to the district, according to Education Week.

“We are heading toward a dual school system: one, privately managed and free to choose and exclude students; the other, public, which must take all kids,” NYU professor and education blogger Diane Ravitch told Forbes recently. “Billionaires support the privately managed sector, in part because they love the fact that 90 percent of charters are nonunion.”

Despite the critics and potential downsides, charter schools keep opening up in LA Unified. The NAPCS report found that growth in LA Unified is in line with a recent report from the California Charter Schools Association, which found that LA Unified saw 33 new charters open this fall, the largest increase in the state.

The state saw the start of 104 charter schools, bringing its total to 1,130. Almost 520,000 California students of more than 6 million now attend charters in the state. Other states with big charter school gains were Arizona, with 87 new ones, and Florida, with 75.

LA Unified continues to lead the growth among school districts, with 32 new charters that serve about 15,000 students, according to the California Charter School Association (CCSA).  There are now 263 charter schools serving 143,580 students in LAUSD. That’s about about 20 percent of the student population.

According to a report issued last month by the CCSA, charter high schools in Los Angeles are outperforming traditional district schools in graduating college-ready students of all backgrounds. Charter schools enroll 19 percent of Los Angeles high school students and deliver 37 percent of the city’s college-ready graduates, the report found.

In California, charters are publicly-funded schools that are generally overseen by local school boards but exempt from some laws governing school districts. While they must operate as non-profit organizations by state law, they receive most funding directly from the state, bypassing the district, thus drawing criticism by supporters of traditional public schools.