Differentiation, an approach to designing and delivering appropriate curriculum and instruction to diverse learners, has been promoted as a means of facilitating student academic achievement. However, little is known about the learning processes by which some teachers develop expertise in differentiation, information important for maximizing teacher skill development. This phenomenological study explored the lived experiences of 8 highly competent and frequently differentiating middle school teachers in a Midwestern public school district to elucidate the events and affective experiences that comprise and inform learning to differentiate well. The primary aim of this investigation was to assess how differentiating teachers describe the process of becoming expert in the practice. A modified version of the Classroom Practices Inventory was employed to select participants who, in audiotaped interviews, shared information on their differentiated instructional practices and knowledge, the events and feelings they experienced while learning differentiation, and their future instructional plans as differentiators. Interview transcripts and memos were analyzed using recursive reading, coding, and pattern identification. Key findings reveal learning and embracing differentiation involves an experiential process of discovery, concept affiliation, and pursuit of additional knowledge, along with possessing a set of affective characteristics that promote resilience and personal investment. This study contributes to positive social change by providing teacher educators with information to improve the design and delivery of instruction to preservice and practicing teachers learning differentiation, thereby enhancing the efficacy of classroom teachers' instructional capabilities. [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.]