American high school students are failing to show overall improvement on a nationwide achievement test, even as they take more challenging courses and earn higher grades, the U.S. Education Department reported.

Nationwide, 73% of 12th-grade students achieved a “basic” reading score in 2005, down from 80% in 1992, according to the National Assessment of Educational Progress, a sampling test the government calls the “nation’s report card.” Sixty-one percent scored at or above the basic level in math.

At the same time, 68% of high school graduates completed at least a “standard” curriculum, up from 59% in 2000, with the overall grade point average about one-third of a letter grade higher than in 1990, the department said in a report. The figures raise questions about the quality of the courses being taught at America’s high schools, it said.

“If, in fact, our high school students are taking more challenging courses and earning higher grades, we should be seeing greater gains in test scores,” Education Secretary Margaret Spellings said in a statement. The results “show that we have our work cut out for us,” she said.

In May, NAEP said there were declines in science scores for high school students. Among 12th-graders, 54% were at or above the basic level in science in 2005, statistically similar to 2000 and a decline from 57% in 1996, the report said.

Business and education leaders said the latest results reinforce fears that the American school system isn’t preparing its students to be competitive in the global workplace.

“It’s disappointing and unacceptable,” said Susan Traiman, director of education and workforce policy at the Business Roundtable, a Washington-based association of chief executive officers of American companies including General Motors Corp., Exxon Mobil Corp., and Citigroup Inc.

“These numbers perfectly bookend the rating of employers last fall,” who in a nationwide survey said more than half of companies finding employees to be inadequately trained in math or reading, said Linda Barrington, labor economist and research director at the Conference Board, a New York-based business group.

Yesterday’s report on reading and math follows President Bush’s release earlier this month of his fiscal 2008 budget recommendation, in which he again asked Congress to devote a greater share of federal funding toward raising high school achievement levels.

Congress hasn’t endorsed that plan in the past, in part because Democrats opposed Mr. Bush’s calls for financing high school improvements through spending cuts in other parts of the federal education budget.

Rep. Buck McKeon, a Republican of California who headed the House education committee last year, believes the NAEP results mean Congress must continue to demand more from schools, spokesman Steve Forde said.

The NAEP report “is a further indication that backing away from that commitment would be a huge mistake,” Mr. Forde said.

Others were more cautious. Some of the lower performance at the 12th-grade level could be due to older students realizing their scores on the NAEP test have no effect on their personal records, said Antonia Cortese, executive vice president of the 1.3 million-member American Federation of Teachers, the nation’s second-largest teacher union.

The federal No Child Left Behind law currently requires schools to test students in grades 3 through 8, then once in high school. Researchers including Bruce Fuller, an education professor at the University of California, Berkeley, have suggested that states may be weakening their tests to help raise their passing rates under the federal law.

The NAEP reports yesterday may reinforce fears that the quality of high-level courses suffers as more students are allowed into them, the Education Trust, a Washington-based research and advocacy group, said in a statement. “This pattern is undoubtedly playing out in some schools,” Education Trust said.