A team of researchers said in a provocative new study that the National Board of Professional Teaching Standards ought to take into account student-learning gains in deciding which teachers are skilled enough to merit receiving its advanced teaching credential. Created in 1987, the board has conferred its credential on nearly 64,000 teachers, and 42 states offer financial incentives to encourage teachers to undergo the lengthy, voluntary certification process. The process draws for the most part on performance-based measures of teaching practice, such as essay responses to pedagogical questions, samples of the written feedback that teachers give students, and videotapes of classroom lessons. In the new paper, though, researchers from Harvard University, Dartmouth College, and the Los Angeles Unified School District make a case for combining the current measures with newer, "value added" calculations that take into account the test-score gains that students make in applicants' classes, or at least lending more weight in the assessment process to the individual tests that link most closely to improved student achievement.