WASHINGTON — 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 seemingly more encouraging research that high school graduation rates in 2012 reached a record 80 percent.

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.

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

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

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.

As in past years, boys did better than girls, but girls outperformed boys in reading.