The primary purpose of this study was to analyze the professional development program at one transitional kindergarten through eighth grade school undergoing a system-wide, major programmatic change. Specifically, how the school organized its professional development opportunities, the frequency in which teachers implemented new learning from the professional development, and how the teachers perceived that these opportunities impacted their classroom instruction. This study was a quantitative case study. In this study, perceptions of professional development and its impact on teacher instruction and student achievement were analyzed by conducting the following: (1) survey questionnaires with participating teachers, and (2) classrooms observations. The setting for this study was a newly formed K-8 magnet school, with a magnet focus of differentiated instruction, located in a K-8 school district in an urban area in southern California. The population in the 2013-2014 school year consisted of approximately 900 students, of which approximately 360 were GATE identified, 40 were identified as special education receiving RSP services and/or Speech services, and the remaining 500 were regular education students. The school employed 34 teachers; 1 RSP teacher, 1 Speech teacher, 1 Intervention teacher, 12 GATE teachers, and 19 regular education teachers. Research suggests that successful professional development follows these steps: 1. Teachers experience professional development. 2. The professional development increases teachers' knowledge and skills, changes their attitudes and beliefs, or both. 3. Teachers use their new knowledge, skills, attitudes, and beliefs to improve the content of their instruction, their approach to pedagogy, or both. 4. The instructional changes that the teachers introduce to the classroom boost their students' learning (Desimone, 2011). The data showed that all teachers that participated in the professional development and completed the survey believed their knowledge and skills had increased. All implemented their new knowledge, to varying degrees and with varying frequency. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]