Many of the nation's biggest urban school districts, including the Pittsburgh Public Schools, slowly are catching up to suburban and rural counterparts in student achievement, according to a study released yesterday.

Pittsburgh made less progress than 25 of 37 urban districts studied; Philadelphia was among those posting better numbers. Overall, student achievement in urban districts remains much lower than that of suburban and rural schools in the same states, raising equity concerns, according to the study by the Brown Center on Education Policy at the Brookings Institution.

At the current rate of growth, urban districts would need a "few more decades" to reach parity with suburban and rural districts, whose achievement levels also have been increasing in recent years, said the author, Tom Loveless, a senior fellow at the Brown Center.

"Progress has been made, but we still have a long way to go," he said.

In 2001, the Brown Center released a report, based on 2000 test data, analyzing achievement in the 37 urban districts and comparing their performance to other types of districts in the same states. The new report, based on 2007 data, gives an update.

The 37 districts collectively scored about 1.26 standard deviations below their states' averages in 2000 and about .77 of a standard deviation below the states' averages in 2007.

In other words, from 2001 to 2007, the 37 districts moved from about the 10th percentile to about the 21st percentile in student achievement among all districts in their states. The "typical big city school district was outscored by 90 percent of districts in its home state in 2000 and by 79 percent of districts in 2007," the study said.

Pittsburgh scored 1.8 standard deviations below the Pennsylvania average in 2000 and 1.68 standard deviations below the average in 2007.

Among Pennsylvania districts, Pittsburgh increased from the fourth percentile to the fifth percentile in student achievement. In 2000, 96 percent of districts statewide outscored Pittsburgh; in 2007, 95 percent did so.

The district did not respond to a request for comment on the study. In 2007, the district was in the early stages of Superintendent Mark Roosevelt's school-improvement campaign.

New Orleans posted the biggest gains since 2000, but Dr. Loveless cautioned that Hurricane Katrina forced out many of the district's poorest, most troubled students.

Dr. Loveless said districts' improvement strategies are too numerous and varied to determine which ones are driving student achievement, but he said he believes the federal No Child Left Behind Act has played some role. He said he'd like to develop a system for identifying effective improvement techniques.