New York State is in the midst of vast education reform. This Education reform has produced an environment in which the traditional roles of school personnel have been restructured and standards of accountability have been increased. Teacher leadership has become a vital force in the success of many organizations. Additionally, the rigorous teaching standards of National Board of Professional Teaching Standards denote accomplished teaching, a prerequisite to teacher leadership. The purpose of this mixed method study was to explore the relationship between accomplished teaching through National Board Certification for teachers and teacher leadership in New York State. This study measured the extent to which the achievement of National Board Certification for Teachers promotes teacher leadership in the hope that substantive change, resulting in increased student learning and achievement, will be promoted and supported in the future. The methods employed by this study were both quantitative and qualitative in nature. The population consisted of middle and secondary teachers in New York State. A sample of 426 National Board Certified teachers and a control group of 511 non-NBC teachers were electronically surveyed. In addition, a random sample of 15 NBCTs were chosen to further elaborate on their perceptions and roles of teacher leadership. Five principals from districts with a high concentration of NBCTs were also interviewed. This study may provide useful information to school and district administrators, as well as aspiring teacher leaders, NBCTs, and National Board Certification candidates as they work to enhance the professional practices within their organization in an effort to meet the constantly changing demands of the current educational reforms and simultaneously ensure that student achievement continuously grows. Teacher preparation programs may also find this information useful as they prepare future teachers for the evolving profession of teaching. [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.]