The teacher has been identified as one of the most important factors in effecting student achievement. Consequently, school systems across the country engage their teachers in costly and time-consuming professional development in an effort to improve their effectiveness. This study examined whether one such professional development activity, the increased presence of National Board Certified Teachers (NBCTs), related to student achievement, and whether there was a certain number of NBCTs that is needed to create a critical mass to positively affect student achievement in a school. In addition, this study examined Maryland elementary school principals' perceptions of NBCTs as it related to improving student achievement, developing effective teachers, making a difference in high-needs schools, retaining accomplished teachers, and growing teacher leaders in order to create school-wide improvement. The design of this study was two-pronged. The first part examined the association between the increased presence of NBCTs and school-wide student achievement in grades three through five as measured by the Maryland School Assessment (MSA). The second part examined the perceptions of Maryland elementary school principals regarding NBCTs' effect on school improvement. The researcher found that the presence of NBCTs was significantly related to the gains in all areas of the MSA. There was not enough evidence to determine the number of NBCTs needed to create a critical mass. The survey demonstrated that principals' perceptions of the National Board Certification process are positive; however, they did not directly attribute the increase in achievement scores to the presence of National Board Certified Teachers. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]