As policymakers over the past decade focused on closing the achievement gap between white students and underrepresented minorities, another rift was widening: the gap between Asian American students and everyone else.

A new study from the Center on Education Policy underscores how significantly Asian American students outpace their peers, particularly in Maryland and Virginia.

The data focus on student achievement on eighth-grade state standardized tests, including a rare analysis of student performance at advanced levels. It is at those levels that the exceptional — and rapidly improving — achievement of Asian American middle- schoolers was most pronounced.

Nationwide, the percentage of Asian American students scoring in the upper echelons on math exams was 17 points higher than the percentage of white students. Notably, that gap has continued to widen in more recent years. In Virginia, for example, Asian American students’ advanced-level math performance leapt from 59 percent to 76 percent between 2006 and 2009, compared with an increase from 43 percent to 58 percent for white students.

In Maryland, that same pattern was apparent on reading tests. The percentage of Asian American students who tested in advanced levels grew from 40 percent to 58 percent between 2006 and 2009. The percentage of white students in that category grew from 35 percent to 48 percent.

“The lesson for other groups is that effort counts. Asian American students are working harder, doing better and getting ahead,” said Jack Jennings, president of the Center on Education Policy.

In Fairfax and Montgomery counties, Asian American students outperform their white peers at the advanced level in several subject areas, but those gaps do not appear to be growing at the same pace as in the rest of their states or the nation.

Fairfax officials said they hadn’t studied the issue. “When we look at the achievement gap, we look at white and Asian students on one side, and African American and Latinos on the other,” said Fairfax County Public Schools spokesman Paul Regnier. “That particular gap isn’t something we’ve looked at specifically.”

Jennings points out that the Asian American subgroup is an imperfect monolith — including students whose families hail from countries as diverse as Japan and Jordan. There are clear disparities within the subgroup. Pacific Islanders, for example, don’t perform as well as Korean students on standardized tests.

But in most states, Asian Americans — sometimes labeled a “model minority” — outperformed all other subpopulations. Some scholars are quick to argue against that label, saying it plays down the diversity, and the challenges, that pervade the subpopulation.

“In reality, there are significant numbers of Asian American and Pacific Islander students who struggle with poverty, who are English-language learners increasingly likely to leave school with rudimentary language skills, who are at risk of dropping out, joining gangs and remaining on the margins of society,” said a 2008 report, “Facts, Not Fiction: Setting the Record Straight,” from the National Commission on Asian American and Pacific Islander Research in Education.

The achievement gap is most commonly measured by the number of students who are considered “proficient” in a given subject. By those measures, the gap between historically underperforming minority groups and white students is shrinking in eighth grade, according to the study. But when the data focuses on achievement at advanced levels, the gap is widening — between white and Asian students, but also between African American and Hispanic students and their white peers.

“It looks like we’re raising the bottom, but not so much helping students in the middle get to the top,” Jennings said.

sieffk@washpost.com