WASHINGTON -- Elementary school children are getting better in science, but middle and high school students are not, a blow for a nation wary about losing its competitive edge.

Federal test scores released Wednesday indicate that fourth-grade students posted small gains over the past five years, mostly through improvement by the lowest-performing children.

The progress was interpreted by education officials as a sign that greater attention to elementary students' math and reading skills -- as demanded by the No Child Left Behind law -- may also be helping in science.

The test found students in grades eight and 12 failed to improve at all since 2000 in their knowledge of earth, physical and life sciences.

The high school seniors actually did worse in science when compared with scores of a decade ago. Almost half of the 12th-graders taking the test in 2005 fell short of showing basic science skills.

"We need to get busy. And that starts with ensuring that all students have access to a strong science curriculum and the teachers with the skills and knowledge to teach science well," said Kati Haycock, director of the Education Trust, which advocates for poor and minority children.

The science scores are from the 2005 National Assessment of Educational Progress, a federal test given periodically on a range of topics. It is considered the best yardstick of how U.S. students perform over time and of how states stack up against each other.

In a positive step on a national priority, black and Hispanic students narrowed their achievement gaps with whites in fourth grade. So did poor students compared with richer ones.

That good news was limited. The racial and ethnic achievement gaps did not shrink in eighth grade, and the gap between blacks and whites only got bigger among 12th-graders.

Education Secretary Margaret Spellings said the results show why the No Child Left Behind law, which focuses on early and middle grades, should be expanded in high schools. The law requires testing in math and reading, with penalties for many schools that fail to improve.

State science testing under the law will begin in 2007-08, although schools will not face consequences for their performance -- something President Bush wants Congress to change.

"The answer is more accountability, not less," Spellings said.

Science skills have become critical in a huge range of blue-collar and white-collar jobs, and they form the foundation of engineering, technology, medicine and other leading fields.

Only 30 percent of 12th graders took biology, chemistry and physics during their high school years.

On the test, most students in each grade could not handle challenging subject matter.

At that skill level, known as proficient, a fourth-grade student can explain what can be learned from fossils. An eighth-grader can identify the location of a cell's genetic material, and a 12th-grader can design an experiment to compare various heating times.

Only 29 percent of students in grades four and eight scored proficient or better, and only 18 percent of 12th-graders did. Larger numbers showed basic skills.

The lackluster performance by older children underscores a deep concern among political and business executives, who see eroding science achievement as a threat to the U.S. economy.

National leaders want to create the same level of urgency around science that existed during the Cold War space race. For symbolism, education officials released the test scores at the National Air and Space Museum, surrounded by replicas of rockets and space shuttles.

The scores were announced by Darvin Winick, chair of the independent National Assessment Governing Board, who said it is natural to see improvements among younger students first. "The good expectation is that when the good kids get to eighth grade or 12th grade, they will do better," Winick said, adding: "That's a wish."

For all the concern at the federal level, the rhetoric has not reached the state and classroom, said Mike Padilla, president of the National Science Teachers Association. "This is where the changes in science teaching and learning are desperately needed," he said.

Students were challenged to understand the principles of science, use their skills to investigate and apply science knowledge to solve everyday problems. Topics ranged from concepts of air and space to energy and motion to the functions of living organisms.

Although the main bright spot was that fourth-graders posted a better overall test score, the percentage of students who could handle challenging work did not improve in fourth grade.

A representative sample of more than 300,000 students in public and private schools took the test. State results were also presented for public schools only in grades four and eight, revealing that most states did not improve over the last five years.

The states posting the highest number of children who could handle challenging science material include Massachusetts, Montana, New Hampshire, North Dakota, Vermont and Virginia.

Among states with the lowest percentages of children doing proficient work are Alabama, Arizona, California, Hawaii, Louisiana, Mississippi, New Mexico and Nevada.

The federal science test is voluntary for states, and six did not take part: Alaska, Iowa, Kansas, Nebraska, New York and Pennsylvania, along with the District of Columbia.

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On The Net:

Nation's Report Card: http://www.nationsreportcard.gov

National Science Teachers Association: http://www.nsta.org/

National Assessment Governing Board: http://www.nagb.org/