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 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.

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. Designed to develop critical thinking […]