For the past decade, students at California State University (CSU) campuses increasingly lack basic mathematics skills. To address this concern, Executive Order No. 665 (1998) called for CSU campuses to bring students to proficiency in mathematics. School districts have struggled to modify their mathematics curriculum, pedagogy, and assessment in response to guidelines established in the Federal "No Child Left Behind" educational mandate. As a result, effective mathematics teaching has become narrowed by boundaries created in the name of educational reform. The importance of mathematical teaching has been heightened, but also limited to a focus on an "algorithmic" platform, leaving fewer students with a "conceptual" understanding of the mathematics. The literature review for this study indicated that success in college level mathematics classes requires a rich foundation in both conceptual understanding and procedural fluidity at high school level mathematical courses. Teachers Assisting Students to Excel in Learning Mathematics (TASEL-M), a data driven program, was generated to improve students' academic performance by providing teacher knowledge and tools to diagnose deficiencies and transform the culture of mathematical departments. This study investigated if the TASEL-M project had the intended effect on student achievement, by looking at participants' mathematical knowledge, attitudes, and practices; and change effects on the professional culture of mathematics departments. The research investigated whether TASEL-M support of classroom teachers increased instructional proficiency in Algebra I, resulting in increased student achievement; and if teachers changed attitudes toward collaboration and use of student data. The teachers who participated in this study were actively engaged in professional development, demonstrated a willingness to share classroom experiences, and improved their content knowledge. Quantitative methods involved the use of achievement data and a survey about professional development. Qualitative methods included surveys, classroom observations and interviews with teachers, coaches, and administrators. The data analysis suggested that implementation of TASEL-M strategies improved instructional proficiency. Another significant finding from the data indicated that having a mathematics coach from outside their school, not a teaching colleague, made the most instructional impact in the classroom. Conclusive findings of this study support mathematics professional development which emphasizes collaborative efforts at all levels to improve teacher effectiveness and student understanding. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]