I examine a unique Elementary Mathematics Lead Teacher program entering its second decade of operation. The program is based in a large, urban, Midwestern school district, with the vision of developing a cadre of teacher leaders to support mathematics education. The district's professional development content was conventional, including both mathematical and pedagogical content knowledge, as well as, leadership and supportive skills. However, their approach to Lead Teachers' functional roles was not typical. Lead Teacher roles were not predetermined; rather roles were expressly expected to emerge and evolve according to each Lead Teacher's circumstances. I investigated these roles, and their evolution. My research questions and conceptual framework sprouted from four areas of knowledge: mathematics education reform, teacher leadership, professional development, and education policy. I also drew on Darwin's Theory of Evolution, and on components of Social Darwinism. Data sources included existing data from the district's files, and data collected in 2009 via my questionnaire, interviews and observations. I utilized three levels of data analysis: a descriptive account, a higher level of category construction, and an in-depth investigation employing case studies. I investigated the environmental stresses and pressures impacting roles as they related to the entire program and to individual participants. The study produced several outcomes: in-depth documentation of a unique Lead-Teacher program; a record tracing Lead-Teacher role progression over an extended period; as well as, the development of an investigative framework for the study of role evolution. Finally, this study lends credibility to the district's atypical approach to the development of Lead-Teacher roles. I therefore, contend it is more beneficial to allow Lead-Teacher roles to emerge, develop and adapt "naturally" to the Lead Teachers personal and school contexts, rather than the typical approach to prescribe or "domesticate" these roles. [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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]