Fewer than half of Virginia 4th and 8th graders are proficient in math and reading, according to national test scores released Tuesday. But Commonwealth students’ performance has inched up in math and continues to outpace the national average in both subjects.

The news comes from the 2011 National Assessment of Educational Progress, also known as the nation’s report card. Given to a representative sample of students every two years since the 1990s, it is widely regarded as the best tool for comparing academic performance over time and across state lines.

Virginia eighth graders’ math proficiency rate is up 4 percentage points since 2009 and now stands at 40 percent. Fourth graders’ math performance also improved: 46 percent are proficient now, as opposed to 43 percent two years ago.

Patricia I. Wright, Virginia’s state superintendent, attributed the math gains to efforts to make the Standards of Learning more rigorous.

“The 2011 NAEP results confirm the gains we have already seen on middle school and Algebra I SOL tests,” she said in a statement.

Reading is a different story.

Virginia students’ reading achievement in 2011 was “statistically similar” to 2009, according to a release from the state department of education. Thirty-nine percent of fourth graders and 36 percent of eighth graders are proficient. Eighth graders’ achievement has been flat since 2003.

State results — math scores up, reading scores stagnant — mirror national trends, which triggered a sober reaction from U.S. Education Secretary Arne Duncan.

“The modest increases in NAEP scores are reason for concern as much as optimism,” Duncan said, according to my colleague Lyndsey Layton. “While student achievement is up since 2009 in both grades in mathematics and in eighth grade reading, it’s clear that achievement is not accelerating fast enough for our nation’s children to compete in the knowledge economy of the 21st Century.”

In Virginia, about 7,600 4th graders and 5,500 8th graders were administered the test. NAEP results aren’t reported for individual school districts or schools.