In this paper, we describe the results of the first large-scale study, based on a unique data set from North Carolina, assessing the relationship between the certification of teachers by the National Board for Professional Teaching Standards (NBPTS) and elementary- level student achievement. Our findings indicate that NBPTS is successfully identifying the more effective teachers among applicants, and that NBPTS-certified teachers, prior to becoming certified, were more effective than their non-certified counterparts at increasing student achievement. The statistical significance and magnitude of the "NBPTS effect," however, differs significantly by grade level and student type. (Publication updated on web 4/7/05)