This is a quasi-ethnographic (qualitative) interview examination of understanding teacher professional development for urban and suburban high school mathematics teachers. Since teacher professional development has been found to be critical in improving student learning such as mathematics achievement, and teacher professional development is recommended by the scholarship as a strategic approach to improve teacher quality through the improvement of teacher practice, the purpose of this research was to study the professional development experiences of four high school mathematics teachers. Two of the teacher participants taught in urban, public school districts and two taught in a suburban, parochial school. Each participant was interviewed three times to understand and describe how teacher professional development proceeded in this study and how teacher participants applied what they learned from their teacher professional development in their classrooms. Cyclical data analysis strategies were used to describe the teacher participants' professional development experiences. A discussion of findings includes descriptions of the outcomes of the teacher participants' professional development experiences with respect to their learning, changes in teacher practice, and students' learning. Additionally, concepts and practices associated with professional learning communities were found to exist in this study and among the teacher participants. [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.]