The purpose of this study was to explore the perceptions of physical education (PE) teachers on the participation of middle-school girls in PE courses. Investigating the perceptions of educators who have direct experience with mixed-gender middle-school PE courses provided new contributions to the limited understanding of engagement and participation among adolescent girls in PE and offered recommendations to increase participation by focusing on the tenets of Self-determination Theory (SDT). This study describes how incorporating SDT as a framework into teaching practices for PE can yield positive outcomes for adolescent girls by increasing participation and engagement. A qualitative research design was chosen to describe the experience of middle-school PE teachers in the study. Four themes that emerged from the data during the analysis for this study were Autonomy, Competence, Motivation, and Relatedness. Participants shared perspectives and knowledge of the behaviors of middle school girls in class that directly relate to each of the four components found in SDT. The findings can positively impact the engagement and participation of middle school girls by contributing to future teacher education courses and instructional training that highlights methods in which instructional practices can incorporate the principles of SDT. [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.]