Results from a national exam revealed that fewer than one-third of elementary- and high-school students have a solid grasp of science, triggering anxiety about U.S. competitiveness in science and technology.

The scores from the 2009 National Assessment of Educational Progress, released Tuesday, come just a few weeks after an international science test showed U.S. students trailing their counterparts in many European and Asian countries. On that exam, called the Program for International Student Assessment, students in Hong Kong and Shanghai dominated their counterparts in the U.S. and most other countries.

Science Test Scores See where students performed higher or lower than the national average, or not significantly different from the national average, on the 2009 National Assessment of Educational Progress science test.

Teachers and education-advocacy groups offered several explanations for the dismal scores on the NAEP exam given to students in fourth, eighth and 12th grade. Reasons included shortages of qualified science educators and of advanced science classes in low-income and rural schools.

Many blamed the lackluster showing on No Child Left Behind, the 2002 federal law that requires schools to test students in math and reading, but not science. These critics contend that schools narrowed their focus to comply with the law.

"Science has been left off the national agenda for too long, and now we are paying the price," said Francis Eberle, executive director of the National Science Teachers Association. "We are seeing a persistent degradation of skills, and we've lost a generation of students."

President Barack Obama has made science and math education a national priority, warning that an inability to prepare students for careers in these fields threatens U.S. prosperity.

Mr. Obama launched a $260 million public-private partnership in 2009 to train 10,000 new math and science teachers and replicate successful science programs in classrooms.

U.S. Secretary of Education Arne Duncan said in a prepared statement Tuesday that the "next generation will not be ready to be world-class inventors, doctors and engineers" if results don't improve.

The 2009 NAEP was given to a representative sample of students in 46 states and Defense Department schools overseas. About 318,000 students sat for the exam in the spring of 2009.

The assessment, administered by the U.S. Department of Education, measures students' knowledge in physical, life, earth and space sciences.

The test requires students to apply knowledge across disciplines. It is generally considered tougher than state-administered exams. The test was updated recently to incorporate advances in science, so results can't be fairly compared with past exams.

Scores are translated into four categories: advanced, proficient, basic and below basic. Proficient represents "solid academic performance," NAEP said, while basic shows partial mastery of skills.

Only 31.6% of all students were proficient or better, while fewer than 3% qualified as advanced.

Thirty-four percent of fourth-graders scored at or above proficient. Describing the life cycle of an organism is an example of a skill demonstrated by fourth graders at the proficient level. Thirty percent of eighth graders met the mark, by demonstrating, for example, that they could recognize that plants produce their own food.

Only 21% of 12th-graders scored proficient. Identifying the difference between stars and planets is an example of a skill demonstrated by 12th-graders at the proficient level.

Boys scored higher than girls at all grades and whites and Asians outpaced African-American and Hispanic students. Low-income students posted the lowest scores. Students in cities tended to score lower than those in suburban and rural areas, while students in the Deep South generally scored below students in Northern and Northeastern states.

Alan Friedman, a physicist who sits on the board that oversees the federal exam, said it was "kind of scary" that so few students scored in the advanced category and far too many landed at "below basic." On the 12th grade exam, 40% of students were at the lowest level.

"Science isn't an isolated trade skill," Mr. Friedman said, pointing out that farmers need basic science knowledge to understand genetically engineered crops and voters need it to assess candidates' views on global warming.

Tom Luce, chief executive of the nonprofit National Science and Math Initiative, said enrolling more students in advanced-placement science courses is crucial to U.S. economic advancement. His group, funded by Exxon Mobil Corp., the Michael & Susan Dell Foundation and the Bill & Melinda Gates Foundation, awards grants to schools to help train teachers and enroll more students into these rigorous curricula.

"There are a lot of children out there who could excel in math and science if we just give them properly trained teachers and a shot at challenging material," he said.