Educational achievement disparities continue to affect subgroups based on socioeconomic status, gender, race, and ethnicity. Despite efforts to close the achievement gap, the Black-White performance gap in reading, mathematics, and science scores remains virtually unchanged. The problem is that science educators in the United States receive insufficient professional training on accelerated instruction to bridge the science achievement gaps between European-American and African-American middle school students. Insufficient professional training can perpetuate achievement gaps between student groups. The purpose of this qualitative case study was to explore how professional development focused on accelerated science learning practices can bridge the science achievement gap between European American and African American middle school students in a suburban school district in New Jersey. Burns' transformational leadership and Guskey's professional development theories influenced this research. This qualitative case study aimed to bridge this gap and expand knowledge of school-based transformational leadership practices. Research questions focused on perceptions of accelerated science learning, professional development, and obstacles to closing achievement gaps. Thirteen teachers and 10 administrators participated in this research study. This study collected data through demographic inquiry and semi-structured interviews with a thematic analysis model to examine the data. Codes were collapsed to interpret research questions, and patterns were evaluated to saturation. Findings revealed inconsistent conceptualizations of accelerated science learning but a positive impression of STEM education. Teachers emphasized the need for content-specific professional development to address the science achievement gap. [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.]