Research and practical experience has shown that, more often than not, the professional development opportunities that are provided for teachers are not intentionally structured to meet their individual needs nor do they have a systemic impact on the knowledge base and skill sets of an entire faculty. Furthermore, the continuous pressure that schools face to raise standards and improve performance requires educational leaders to develop and implement school improvement strategies that will lead to increased student achievement. This problem of practice was explored through a qualitative program evaluation of a site-based, differentiated professional development model that is aligned with school improvement goals. This program was implemented at a small, suburban middle school in central Massachusetts. The professional development offerings were differentiated by delivery method, included on-site and off-site sessions, and provided teachers with opportunities to participate in the design of, or make choices related to, their own professional development. This study focused on the participants' perceptions of the development, implementation, and impact of the program as well as its utility as a program for individual growth and continuous school improvement. Data was collected through an end of year survey and focus group. The findings of this study suggest that that this type of professional development model is useful in that it should lead to organizational improvement and capacity building. Additionally, this study revealed four specific components that, when included in a professional development model, can effectively contribute to the professional growth of 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://www.proquest.com/en-US/products/dissertations/individuals.shtml.]