The gap in academic achievement between traditionally underrepresented minority students and their White counterparts remains evident. Therefore, intervention is needed to prompt teachers to reflect and act on their professional development (PD) strategies. This qualitative case study aims to explore K-12 teachers' perceptions of strategies learned in PD and their experiences in utilizing them to drive and differentiate instruction. Sociotransformative constructivism and transformative learning theory were the guiding conceptual frameworks for this study. Three research questions were used to address the concern that effective strategies learned in PD and the experiences in utilizing them in the classroom, through differentiated instruction, support underrepresented students and narrow the achievement gap. Data used in this qualitative case study design were collected from interviews, field notes, observations, and secondary source documents. Participants included two PD coaches and eight teachers. Thematic data analysis was used to identify themes and sub-themes for the results. Teacher change was developed using repertoire that influenced student learning outcomes. Teachers require continual deepening of knowledge and skills. PD provided to teachers that delivers a more personalized approach to learning collaboratively with their peers is what is needed to make a difference in 21st century learning. School leaders and policymakers must make every effort to enforce, reinforce, and sustain PD to close the achievement gap. The current study was intended for policy makers, educators in leadership and administration, and participating teachers to gain information and to inform further adjustment and refinement. [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://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]