Handing out dismal grades, the Nation’s Report Card says America’s high school seniors lack critical math and reading skills for an increasingly competitive global economy.

Only about one-quarter are performing proficiently or better in math and just 4 in 10 in reading. And they’re not improving, the report says, reinforcing concerns that large numbers of today’s students are unprepared for either college or the workplace.

Scores on the 2013 exam in both subjects were little changed from 2009, when the National Assessment of Educational Progress was last given to 12th-graders. The new results, released Wednesday, come from a representative sample of 92,000 public and private school students.

The report follows the just-released and seemingly more encouraging research that U.S. high school graduation rates in 2012 reached 80 percent, a record.

One possible explanation is that lower-performing students who in the past would have dropped out of school are now remaining in the sampling of students who take the exam, said John Easton, acting commissioner of the Education’s Department’s National Center for Education Statistics.

Still, Wednesday’s results are likely to embolden supporters of the Common Core standards that are being rolled out in 44 states and the District of Columbia. They spell out what math and English skills students should master at each grade.

There have been political storms in many states over the standards. Opponents say the standards are untested and would rob school districts of local control.

Bob Wise, president of the Alliance for Excellent Education and a former governor of West Virginia, said the new national results speak to a “desperate need for the aggressive implementation” of the standards.

In reading, the 38 percent share of students performing at or above the proficient level on the test was lower than the 40 percent share when the assessment was first given in 1992. Scores have remained similar since 1994.

Past comparisons in math date only to 2005. Scores had increased from 2005 to 2009.

Even as 12th-grade scores have stagnated, fourth- and eighth-grade students have made slow but steady progress on the exam since the early 1990s. Michael Petrilli, executive vice president at the Thomas B. Fordham Institute, said it’s unclear why younger students are doing better while high school seniors are not.

One possibility is that high school seniors simply aren’t motivated when they take the exam. Another is that students are taking watered-down classes and “all we’ve done is put them in courses with bigger titles,” said Mark Schneider, the vice president at the American Institutes for Research. He is the former commissioner of the National Center for Education Statistics.

At all levels, there continue to be racial disparities. Among high school seniors, white and Asian students scored higher on average in the recent results in both reading and math than black, Hispanic and American Indian students. Asian students scored higher than white students in math but did not do significantly better in reading.

“We must reject educational stagnation in our high schools, and as a nation we must do better for all students, especially for African-American and Latino students,” Education Secretary Arne Duncan said in a statement.