Differentiating instruction for individual students has been shown to enhance achievement, and professional development has been shown to be an effective method of teacher training. The purpose of this project study was to assess teachers' tolerance for and acceptance of professional development for differentiated instruction in a suburban high school in New York State. Gardner's multiple intelligences and Tomlinson's theory of differentiated instruction served as the theoretical foundations of this investigation. The investigation provided insight into how teachers gained new understandings about student learning to improve their instruction through being part of focused, high quality, and sustained professional development experiences. This descriptive case study was based on the analysis of data from interviews with 10 teachers. These interviews were recorded, transcribed, and analyzed using in vivo coding. Results included themes related to teachers' attitudes toward and confidence in the value of professional development. The themes that emerged were: (1) the teachers' beliefs and attitudes about their abilities to teach and reach all students; (2) the teachers' levels of confidence in meeting the needs of all students; and (3) significant, personal learning experiences that made a significant impression in their lives. That information then led to a model for professional development of differentiated instruction based on teachers' needs through the approaches of technology training, hands-on instruction, and study group collaboration. The results should lead to positive social change, as they may provide teachers with information on new ways to improve students' enhanced inquiry, analytical, and decision-making skills. These skills should lead to greater student learning that will enable students to achieve more in life and experience greater success. [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.]