The purpose of this transcendental phenomenological study is to understand the lived experiences of Mid-Atlantic region public high school teachers participating in onboarding practices, which provides insight into best practices to increase teacher self-efficacy and decrease attrition rates. The theory guiding this study is Albert Bandura's theory of self-efficacy, as it links ineffective and effective onboarding practices for new high school teachers with their levels of teacher self-efficacy, aligning with teacher retention and attrition rates. Bandura's theory of self-efficacy provided a framework with which to answer the central research question and three sub-questions: (CRQ) What are the lived experiences of new high school teachers who participate in onboarding practices? Selected through purposive, heterogeneous sampling, fourteen public high school teachers from the Mid-Atlantic region participated in this study. Data was collected through letter writing prompts, individual interviews, and a focus group. The data was analyzed through the four stages of Moustakas' 1994 transcendental phenomenological design process. From the triangulation of the three collected data types that were coded and synthesized, three universal themes arose to tell the story of the Mid-Atlantic public high school teachers' onboarding experience, leading to three critical findings from the research analysis: (a) new teachers need support through effective peer mentoring; (b) teachers need administrative support; (c) effectual student engagement is needed to sustain teacher self-efficacy. Empirical, practical, and theoretical implications of the data analysis and recommendations for future research are included and described. [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.]