Providing effective professional development that improves teaching quality and in turn impacts student performance, has been of key interest to educational leaders. This qualitative phenomenological collective case study explored the use of microteaching as effective professional development and its effect on teacher instructional practices and behavior over time. Data were collected through a survey about the participants' microteaching experience, video clip interviews from 2019 and 2020, classroom observations, and a follow up questionnaire. Elements of effective professional development found in the microteaching experience that impacted instructional practices, implementation of instructional strategies, or teacher behavior were the key focus for this study. Additionally, participants in this study identified ways in which they learn best, which led to transfer of their learning into the classrooms, thus impacting student performance. Implications from this study suggest that professional development designers, planners, and providers should consider how adults learn best and incorporate those elements to enhance the learning experience. Another implication is that teachers should be able to learn in a way that supports their learning style so implementation of new instructional strategies learned through professional development can be sustained over time. While additional research on microteaching as an effective form of professional development that impacts instructional practices over time is needed, teacher participants in the present study showed that microteaching offers the capability to be a model of professional development flexible enough to provide teachers with differentiated instruction to support their learning and to make an instructional difference over time. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]