In this paper, we describe the results a study assessing the relationship between the certification of teachers by the National Board for Professional Teaching Standards (NBPTS) and elementary level student achievement. We examine whether NBPTS assesses the most effective applicants, whether certification by NBPTS serves as a signal of teacher quality, and whether completing the NBPTS assessment process serves as catalyst for increasing teacher effectiveness. We find consistent evidence that NBPTS is identifying the more effective teacher applicants and that National Board Certified Teachers are generally more effective than teachers who never applied to the program. The statistical significance and magnitude of the "NBPTS effect," however, differs significantly by grade level and student type. We do not find evidence that the NBPTS certification process itself does anything to increase teacher effectiveness. Data tables are appended. (Contains 7 tables, 1 figure, and 49 endnotes.)