WASHINGTON — Schools looking to hire teachers should keep an eye out for those with national board certification.

Students taught by educators certified by the National Board for Professional Teaching Standards make bigger gains on standardized tests than students taught by other teachers, finds a National Research Council report out yesterday.

"I would sure look for the credential," said Milton Hakel, a Bowling Green State University psychology professor who headed the committee that conducted the council review. "The fact that the signal is there is something that's useful to superintendents, to hiring committees, to districts."

It is not clear from the research whether the process of getting certified by the national board makes teachers better or if those who get certified were already top performers, according to the report. More research is needed to try to determine that, Hakel said.

Joseph Aguerrebere, president and CEO of the board, said the report puts to rest the question of whether board-certified teachers are more effective at boosting student scores than others.

"It's a question that we're often asked," he said.

Schools have been increasingly focused on student test scores since the 2002 No Child Left Behind law was enacted. A goal of the law is to get all students working at their proper grade level in math and reading, according to standardized tests, by 2013-14.

The research council, an arm of the National Academy of Sciences, based its findings on a review of existing research and on some of its own analysis.

The national board is a nonprofit that, for more than a decade, has set standards for what accomplished teachers should know and be able to do and then certifies those who meet the standards.

It generally takes teachers a year or more to get through the certification process, which includes taking subject-area tests and submitting on-the-job videotapes and samples of student and teacher work.

It costs about $2,500 to accredit each teacher.

Just 64,000 teachers have earned the accreditation, which amounts to a mere three teachers in every five schools, according to the report.

While teachers have to be licensed by their states, national board certification is voluntary.