Paintings of James Baldwin, Malcolm X and the Rev. Martin Luther King Jr. are seen in a hallway at D.C.’s Maya Angelou Public Charter School in 2011. (Matt McClain/FOR THE WASHINGTON POST)

The District has the nation’s fourth-highest concentration of charter school students, behind New Orleans, Detroit and Flint, Mich., according to a report from the National Alliance for Public Charter Schools.

Three years ago, only New Orleans — where Hurricane Katrina had destroyed the traditional public school system and where more than nine in 10 children now attend charters — had a greater percentage of students in charter schools than the District.

But as enrollment in the District’s traditional school system has grown in the past several years, the market share of the city’s charter schools has stayed relatively flat.

The District’s charter school share was 44 percent in both 2013-2014 and 2014-2015, and raw enrollment data for the current school year suggests that it isn’t changing.

That flat-lining comes after a period of rapid growth: Nine years ago, just 25 percent of D.C. schoolchildren were in charters, which are funded with taxpayer dollars but run by independent nonprofits.

Nina Rees, president and chief executive of the National Alliance for Public Charter Schools, called the city “one of the best examples of a thriving charter public school environment” in the nation.

Elsewhere, particularly in cities where traditional public school systems are struggling, charter schools’ market share is growing more quickly.

In Flint, for example, the percentage of children in charter schools rose from 44 to 47 between 2013-2014 and 2014-2015. In Kansas City, Mo., it increased from 37 percent to 41 percent; in Philadelphia, from 30 percent to 33 percent.

It’s part of a longer-term nationwide trend in which fast-growing charter schools are taking on a significant portion of the students in individual communities, stoking debates about what the rise of charters means for a variety of issues, from school funding to equity.

A decade ago, only New Orleans had 30 percent or more of its students in charter schools. Now, 14 cities have hit that benchmark, and six have surpassed the 40 percent mark, according to the alliance.

Nationwide, 2.9 million students attended charter schools in 2014-2015, up 14 percent from the year before.

Los Angeles had 151,000 students in charters, far more students than any other city, although — because L.A. is so big — they accounted for just 23 percent of the overall student population.

New York was second-highest with 84,000 children in charters. The District had close to 38,000 students in charters.