The study examined the effect of National Board Certified Teachers (NBCTs) in instructional leadership roles, operationalized as mentors to novice teachers, on (a) classroom practices of mentored novice teachers in Grades K-12 and (b) student achievement of mentored teachers' students in Grades 4-8. The study compared outcomes between NBCT mentors and non-NBCT mentors. The study examined the effect of NBCT mentors after one academic year and was conducted in San Francisco Unified School District. Using the Classroom Assessment Scoring System, we examined novice teachers' classroom practices on the domains of Emotional Support, Classroom Organization, Instructional Support, and across all three domains. The results did not reach statistical significance, but the effect sizes for Emotional Support, Classroom Organization, and a global measure across all domains suggest meaningful differences between classroom practices of novice teachers mentored by NBCTs and non-NBCTs. These effect sizes were 0.28, 0.28, and 0.21 standard deviations, respectively. The effect size for the domain of Instructional Support was near zero at -0.06 standard deviations. Our sample size for the analysis of classroom practices did not have sufficient power to estimate differences at a statistically significant level. We examined student achievement using the state's standardized test scores in mathematics and English language arts. Our achievement measure includes either subject: That is, we did not estimate effects separately for mathematics and English language arts. The results suggest that students taught by teachers mentored by NBCTs had a higher level of achievement than students mentored by non-NBCTs. The difference was statistically significant at a p value of 0.05, and the effect size was meaningful at 0.18 standard deviations. Small sample sizes and low statistical power prevent us from making confident conclusions about the effect of NBCTs in instructional leadership roles on classroom practices of supported teachers and student achievement. However, the evidence is encouraging and warrants additional rigorous research on the impact of NBCTs as instructional leaders.