Professional development is vital to PK-12 teachers' growth and student learning, contributing to school improvement (Barghani, 2021; Bredeson, 2000; Darling-Hammond, 2000; Snow-Renner & Lauer, 2005). Yet, with all the systems that have been put into place by NCLB (2001), and ESSA (2015) to provide PK-12 teachers with effective professional development, there are still not enough effective models to be considered the standard of practice in the United States. The purpose of this qualitative phenomenological study was to examine PK-12 teachers' perceptions of the professional development they have received and are expected to implement into their instructional practice to help increase student learning. Twelve, PK-12 teachers from the Northeast, South, Midwest, and West regions of the United States participated in the study. Semi-structured interviews were conducted to gain insight into their lived experiences of the professional development they have experienced throughout their teaching careers. Listening to PK-12 teachers reflect, allowed the researcher to capture the essence of those experiences. The findings of this study reveal that while PK-12 teachers have experienced some effective professional development, it has been inconsistent. PK-12 teachers shared their need to have more input into the decision-making to ensure that professional development is continuous and relevant to their content and demographic needs. They also shared a desire for more opportunities to actively engage and collaborate with peers. The Conceptual Framework of Desimone (2009) is recommended to the educational community of PK-12 teachers, to adopt and tailor to their specific needs. The framework consists of five factors, content focus, active learning, duration, coherence, and collective participation that contribute to effective professional development. This conceptual framework is suggested to help combat ineffectiveness in the professional development of PK-12 teachers. [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.]