We study the effectiveness of teachers certified by the National Board for Professional Teaching Standards (NBPTS) in Washington State, which has one of the largest populations of National Board Certified Teachers (NBCTs) in the nation. Based on value-added models in math and reading, we find that NBPTS certified teachers are about 0.01-0.05 student standard deviations more effective than non-NBCTS with similar levels of experience. Certification effects vary by subject, grade level, and certification type, with greater effects for middle school math certificates. We find mixed evidence that teachers who pass the assessment are more effective than those who fail, but that the underlying NBPTS assessment score predicts student achievement. Finally, we use the individual assessment exercise scores to estimate optimal weights for value-added prediction.