In today's workforce, individuals are staying in their respective professions longer and retiring at ages past 67, resulting in a generationally diverse workforce. Currently, teachers range from 21-80 years of age, working in the same profession and receiving the same professional development. Considering adult learning and the dynamics associated with individuals, it is important to understand that, historically, the professional development provided to this workforce is facilitated in a one-size-fits-all arrangement (Gregson & Sturko, 2007), instead of using diverse adult learning styles (Malik, 2015). The purpose of this study is to understand individual teachers' perceptions of the efficacy of professional development received in a high school education setting. Additionally, this research focuses on generational differences and how these differences may impact the learning environment for high school teachers. The study utilized a qualitative instrumental case study. The participants were teachers, Grades 9-12, in a Central Texas high school, who fall into one of the following generations: Baby Boomers, Generation X, and Millennials. [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.]