Achievement gaps between advantaged and disadvantaged students on state tests have narrowed in many instances over the past decade—continuing a trend that appears to have been bolstered in the 1990s by the standards-based-reform movement, concludes a wide-ranging analysis released today.

The study from the Center on Education Policy analyzes the achievement gap between low-income students and their peers, and between minority and white students, using test data from all 50 states collected from 2002 through 2008.

Viewing those gaps through a variety of lenses, the report finds that, on the whole, the disparities appear to be narrowing because of the accelerated achievement of lower-performing groups, not slower progress by high-achieving groups. Nevertheless, achievement gaps continue to remain as large as 20 percentage points or more in some states, the report indicates.

“By no means are we saying that we’re in nirvana; there’s a long way to go,” said Jack Jennings, the president of the Washington-based research group. “But as a nation, if we ask schools to narrow the achievement gap and that’s what the schools are doing, we should give them credit for it.”

The report notes that the overall phenomenon of narrowing gaps appears consistent with long-term data from national assessments in reading and math, which show low-income and minority students narrowing the gap with their more-advantaged and white peers since the early 1970s. Gaps widened again in the 1980s, only to appear to begin closing again after 1999, the national data show.