D.C. public schools have the largest achievement gap between black and white students among the nation’s major urban school systems, a distinction laid bare in a federal study released Wednesday.

The District also has the widest achievement gap between white and Hispanic students, the study found, compared with results from other large systems and the national average.

The study is based on the 2011 National Assessment of Educational Progress, federal reading and math exams taken this year by fourth- and eighth-graders across the country.

The tests are the only continuing and nationally representative assessment of what students know. State-by-state results were released last month, but large cities have agreed to have their results published separately since 2002, with 21 participating this year.

Generally speaking, the results in large cities mirror national trends: Students show some improvement in math, but progress in reading is stagnating.

In reading and math, the gaps in scores between black and white students were widest in D.C. schools compared with those in 20 other urban systems, including New York, Los Angeles and Miami.

The D.C. gap was also greater than the national average and the average for cities with populations of 250,000 or more, according to the study.

On the fourth-grade math test, for example, black students in the District scored an average of 212 points out of a possible 500, and their white classmates averaged 272. That 60-point difference is more than twice the national achievement gap for that test.

The achievement gap has been a stubborn problem and of growing concern among educators, policymakers and civic leaders. With enactment of the No Child Left Behind law in 2002, the federal government made closing the gap a priority and a reason for increased accountability in public education. Many strategies have been deployed by schools across the country to attack the gap, but few have resulted in substantial progress. All the cities analyzed for racial and ethnic performance gaps found differences between whites and blacks and between whites and Hispanics.

But in every case, their variations were narrower than in the District — in some cases, five times smaller. In the fourth-grade math example, for instance, Cleveland’s black and white students were separated by 21 points.

The District’s racial gap is really an income divide, said Michael Casserly, executive director of the Council of the Great City Schools, which represents the largest urban school systems.

“You’ve got relatively more well-to-do whites in Upper Northwest quadrants, particularly Ward 3, which score higher than white students nationally, and you’re comparing it with poor, African American students largely in wards 7 and 8,” Casserly said. “There are extreme income disparities.”

Although Cleveland appears to have a narrow racial gap, the small difference between black and white students’ test scores is linked to the fact that both groups are relatively low-income, Casserly said. “You’ve got poor Appalachian whites in Cleveland and poor African American students,” he said.

In addition to income, black and white adults in Washington are separated by educational background, said Amy Wilkins of the Education Trust, an advocacy group focused on narrowing the achievement gap. “D.C. is in many ways a tale of two cities,” she said. “The mostly white parts are among the best-educated in our populace — overeducated people with multiple degrees — people who come here to work on the Hill or for Brookings or wherever.”

To narrow the achievement gap, the city should spend more heavily on schools in poor neighborhoods, she said.

“We need to make sure the kids who have the least, who don’t have parents who can take them to France or Yosemite on summer break, who can’t afford a computer . . . get the most resources and schools in Cleveland Park, frankly, get less,” she said.

D.C. Schools Chancellor Kaya Henderson said the study was not a surprise because the scores tracked with the District’s data. The city is planning a “robust” set of interventions, including a new curriculum and better teacher training, she said.

“We believe we have put the pieces in place to radically change these results and close the gap,” she said.

The District’s racial achievement gap is long-standing.

But it’s difficult to say whether that gap has changed over time relative to that in the other cities because for much of the past decade, there haven’t been enough white students in the District taking the test to reliably draw conclusions, according to the National Assessment Governing Board, which sets policy for the test.

There are 46,191 students in the District’s public schools, with about 79 percent African American, 12 percent Hispanic, 7 percent white and 2 percent self-declared “other.”

The new study did not include test scores of students who attend D.C. public charter schools, which educate about 40 percent of the city’s public schoolchildren. An analysis of the test scores of D.C. public charter students this year showed that black students attending charters scored higher in math and reading tests in the fourth and eighth grades than did their counterparts in traditional District schools. The number of white students attending public charters in the District was too small to draw comparisons.

Overall, the District placed at or near the bottom of the 21 cities in the study in scores for math and reading in the fourth and eighth grades; Washington tied with Detroit for last place in eighth-grade reading.

The school systems that consistently scored at the top of the heap were Charlotte, which was either No. 1 or 2 in every category; Hillsborough County, Fla.; and Austin.

Staff writer Bill Turque contributed to this report.