The advanced teacher certification offered by the National Board for Professional Teaching Standards effectively identifies teachers who are highly skilled, but may not have improved the quality of teaching, according to a report released today by the National Research Council.

Milton D. Hakel, a professor of psychology at Bowling Green State University who served as chairman of the committee that wrote the report, said in a written statement that the board’s advanced certification “is a useful ‘signal’ that a teacher is effective in the classroom.” His committee found that students who are taught by teachers certified by the board make greater gains on achievement tests than students whose teachers lack such certification.

“But,” Mr. Hakel said, “we don’t know whether the certification process itself makes teachers more effective — as they become familiar with the standards and complete the assessment — or if high-quality teachers are attracted to the certification process.” The report recommends additional research to answer that question and to determine whether the board’s certification is having an impact on the nation’s education system beyond the classrooms of teachers who earn the credential.

To earn certification from the board, teachers must complete six computer-based exercises and assemble a portfolio showing they have met certain standards. Since 1993 more than 99,000 teachers have applied for such certification, and more than 63,000 have earned it, meaning that there now are about three board-certified teachers for every five schools in the United States. —Peter Schmidt