Educators across the U.S. participate in professional development (PD) to improve their teaching competencies. Numerous legislatures have mandated PD to develop highly qualified teachers; however, literature on PD has shown that teachers feel PD does not meet their needs. With consideration for the diverse needs of teachers, in this study I sought to understand middle school teachers' perceptions in one public school district in Florida regarding the effectiveness and relevance of mandated PD during school improvement time. Using an explanatory sequential mixed methods design, I collected data through an electronic questionnaire (n =21) and interviews (n = 7) to answer the question: What are middle school teachers' perceptions of the effectiveness and relevance of district-mandated PD? The questionnaire results indicated teachers' felt PD is effective when it focuses on content, is collaborative, and is coherent. Furthermore, teachers described PD that was applicable to the classroom and aligned to the needs of their school and students was relevant. I used interviews to explain these results further and found that content focus was lacking due to an emphasis on PD related to testing. Additionally, teachers explained that collaboration with teachers both in and outside of the content area they teach is effective. In contrast, the confusion teachers had regarding the planning of topics and PD led to them longing for coherence. After triangulating the data, I found teachers explained application as the ability to immediately use the training or resource without having to adapt it themselves. Furthermore, teachers elaborated that when PD is led by someone who has been in the classroom, understands their school, or teaches the same subject as them, they find it relevant. Teachers also shared that PD was focused on testing when it should be focused on topics related to content or student behaviors that have resulted from COVID-19. Findings from this study will benefit future educators and district personnel as they prepare for upcoming PD opportunities to address the needs of teachers within their district. [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.]