Many school districts in the United States struggle to retain assistant principals (APs), thus losing the opportunity to prepare and promote quality internal candidates for the principalship. The purpose of the critical participatory action research study was to add to the limited research on AP experiences and how to support their professional development in a way that successfully leads APs to the principalship. The research aimed to add qualitative data from APs employed in public school districts in Ohio to provide much-needed insight into how to better retain school administrators and create an internal candidate pool of highly qualified school principals. The research questions centered around providing insights into AP on-the-job socialization and experiences that impacted their career path decisions and gathered their recommendations for school districts when creating a principal pipeline program or other intentional supportive professional development opportunities for APs. Purposive, stratified/cell sampling was used to collect data from homogeneous participants who share a geographic location (state) and the same biographical background of making lateral career moves as APs of one school district to another, but are considered representative of various demographic groups. The APs shared their experiences through semi-structured interviews and made recommendations for how school districts could better support APs and prepare them for a future principalship. The questions encouraged interviewees to employ a systems thinking approach and DSRP metacognitive process to reflect. I used a critical constructivist grounded theory methodology to analyze the data collected through an iterative inductive process of initial and focused coding and memoing combined with input from participants to uncover, compare, and synthesize common themes. Four APs were interviewed, which provided insights into their on-the-job socialization and experiences. Two of the APs participated in a second follow-up interview to offer recommendations for school districts to better support, retain, and prepare APs for a future principalship. Upon analysis and synthesis of the findings, the following themes emerged: relationship building, role clarity, communication, and factors for their career mobility. Two APs provided the following recommendations: 1) provide intentional support and specific targeted training, 2) implement a high-quality mentoring program for APs, 3) utilize best practices for effective one-on-one meetings, and 4) ensure that coaching of APs is carried out with fidelity using the Ohio Principal Evaluation System (OPES). The results of the study's findings led to the development of an action plan focused on improving onboarding, communications, mentoring, and one-on-one meetings to positively impact relationship building, role clarity, and communications thus leading to APs' increased feelings of job satisfaction and longer retention within their school 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.]