Educators today must engage in ongoing Professional Learning (PL) to build competencies beyond their academic content expertise in order to develop and facilitate learning that helps their students to acquire the knowledge, skills, and understandings students need to thrive in a complex, global society. The purpose of this Action Research study was to understand and improve teachers' experiences and engagement with in-house Professional Learning designed to forward the school's vision for teaching and learning, specifically in relation to the articulated diversity, equity, inclusion, and belonging (DEIB) mission at the research site. Participants and data collected in Cycle 1 consisted of teachers at the research site who shared their preferences and experiences with Professional Learning through semi-structured interviews and open-ended survey responses. Action Steps that included assembling a team of faculty collaborators, implementing teacher-led Professional Learning sessions, and facilitating reflection sessions after experiencing DEIB training from an outside organization were designed, implemented, and evaluated in Cycle 2 to understand participants' experience with PL that honored the teacher PL preferences from Cycle 1 findings. Cycle 2 findings suggest that faculty and staff at the research site experienced engagement and motivation with PL activities that were designed to deliver perspective-shaping content, to increase participants' competence in relation to the school's mission-driven DEIB goals, and to offer time to learn and reflect with colleagues in collaborative, active ways. These results relate to the tenets of Self-Determination Theory--"autonomy," "relatedness," and "competence"--and Social Cognitive Theory's concept of collective efficacy. Implications for the research site indicate that school leaders will benefit from (a) continued collaboration with classroom teachers and staff to plan PL experiences (b) clarity for participants regarding the specific mission-aligned competencies they are building through the PL experiences, and (c) honoring participants' desire to learn actively in collaboration with others. [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.]