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 own results published separately since 2002, with 21 participating this year.
Generally speaking, the results in large cities mirror national trends: Students are showing some improvement in math, but progress in reading is stagnating.