In a Midwestern school district, teachers and administrators have specific concerns and opinions about professional development (PD) related to differentiated instruction. Carol Ann Tomlinson, the guru of differentiated instruction (DI), refers to DI as meeting the needs of students by adjusting instruction in order to address how they learn through their interests, the way in which they want to learn, and when they are ready for the next level of learning. Sometimes the content, the process of instructional delivery, or final assignments may need to be altered to differentiate instruction. In this case-study approach, teachers in eight elementary and middle-school classrooms were observed and interviewed about their beliefs concerning teaching and learning in 2006. In 2007, 200 elementary and middle-school teachers, as well as 20 administrators, completed surveys regarding their perceptions of professional development related to differentiated instruction. The survey included three main categories: (a) demographics; (b) degree of implementation of the components of differentiated instruction; and (c) perceptions of professional development needs in educational innovations, such as differentiated instruction. In 2010, repeat data collection was done with three of the original teachers who were observed and interviewed in 2006. In addition, two administrators were interviewed in 2010. The data were triangulated and analyzed using a case-study approach. Survey data were analyzed using descriptive statistics. Observation and interview data were analyzed for patterns and themes using a constant comparative approach. Because learning an innovation involves changing one's behavior for successful implementation, I applied the framework of the Concern-Based Adoption Model (CBAM) to explain how people interact with change. The results of the study include the perceptions of eight teachers and two administrators regarding professional development and differentiated instruction, and the participants' perspectives on how to improve the transfer of professional development training into practical application. The findings from this study, although not generalizable, may prompt others to further research the successful transfer and implementation of professional development, specifically differentiated instruction. Five major themes emerged. First, it was found that the more locus of control a teacher had, the higher the degree of differentiated instruction. The greater the degree of differentiated instruction, the greater the frustration if the teachers perceived that they had no flexibility in making curricular decisions or being trusted to make decisions based on their professional judgment. When teachers who differentiated instruction to a high degree felt they were forced to be compliant because of teachers who did little differentiation, feelings about a lack of respect, trust, and self-efficacy were evident. Unequivocally, the equity of professional development opportunities was a strong theme throughout the data, along with various types of collaboration as the preferred style of learning and professional development. [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.]