Six school districts across the country now have at least 30 percent of their public school students enrolled in charter schools — with Washington D.C. at No. 2 on the list. And 18 systems have more than 20 percent of their students attending charters, according to a new report.

The charter demographics report, released by the National Alliance for Public Charter Schools, lists Los Angeles as topping the list (see below) of districts with the highest number of charter school students — 79,385 (which was 12,576 more this school year than last). If those students were in a single school system, it would be in the top 45 of the largest U.S. school districts.

The growing number of charter school students across the country underscores the popularity among policy makers and school reformers of these institutions as a key lever of school reform. They say these schools offer parents valuable alternatives to traditional public schools that often fail students year after year. In the last two years, 19 states have entirely or partially lifted caps on the number of charter schools allowed to open, and one state, Maine, passed a law permitting charters for the first time.

There are, however, growing concerns among critics about charters. Research suggests that most charters are no better — or worse — than traditional public schools, and questions persist about how well they are monitored by their chartering agencies as well as about the propriety of for-profit groups operating schools to make money.

Issues of access to charters by learning disabled and other children have arisen in New Orleans and other cities, and there have been complaints that some charters force out — against charter rules — students who are disciplinary problems or who can’t keep up with the academic work.

The report, titled “A Growing Movement: America’s Largest Charter School Communities,” says that there are a total of about 1.8 million students in public charter schools.

According to the National Center on Education Statistics, more than 49.4 million students were expected to attend public elementary and secondary schools this school year (with an additional 6 million in private schools). If both of those numbers are accurate, than charter students represent about 3.6 percent of public school students in the United States, though a slightly larger percentage is sometimes given by charter advocates.

The report says that nearly 100 school districts now have at least 10 percent of public school students in charter schools, and among the 50 districts with the largest charter school student enrollment, 19 had growth in the number of students enrolled by 10 percent or more from last school year to this year.

The two with the largest growth — of over 40 percent — were Orange County Public Schools in Florida and Memphis City Public Schools in Tennessee.

The 10 districts with the highest percentages of charter school students are:

* New Orleans Public School System, La., 70 percent

* District of Columbia Public Schools, 39 percent

* Detroit Public Schools, Mich., 37 percent

* Kansas City, Mo., 35 percent

* Flint City School District, Mich, 32 percent

* Gary Community School Corporation, Ind., 30 percent

* St. Louis Public Schools, Mo., 29 percent

* Dayton Public Schools, Ohio, 27 percent

* Youngstown City Schools, Ohio, 24 percent

* Albany City School District, NY, 23 percent

* Cleveland Municipal School District, Ohio, 23 percent

* Toledo Public Schools, Ohio, 23 percent

The districts with the highest number of public charter school students are:

* Los Angeles Unified School District, Calif., 79,385

* Detroit Public Schools, Mich., 45,073

* School District of Philadelphia, Pa. (40,322)

* New York City Department of Education, N.Y., 38,743

* Chicago Public Schools, Ill., 37,909)

* Houston Independent School District, Tex., 37,499

* Miami-Dade County Public Schools. Fla., 35,380

* District of Columbia Public Schools, 29,366

* New Orleans Public School System, La., 27,728

* Broward County Public Schools, Fla., 24,150

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