Recent decades have seen a shortage of qualified secondary school principals. Retirements and an accelerated rate of attrition from the ranks of school leadership has exacerbated this shortage, necessitating an urgency to understand the factors that facilitate the professional development and growth of the next generation of school leaders. The purpose of this study was to use the principles of andragogy and experiential learning to provide a comprehensive description and analysis of the educational and job-embedded experiences that contribute to the development of the skills necessary for assistant principals to advance successfully to the principalship. A phenomenological qualitative research design incorporating focus group interviews and surveys was selected. The participants in this study included 10 entry-year secondary school assistant principals and 10 experienced secondary school principals from the State of Ohio. Participants responded to interview questions exploring constructs related to professional background, post-graduate principal licensure program preparation, influential mentors, and critical on-the-job experiences. The findings of the study identified specific job embedded experiences, specifically those involving crises that occur during the entry-year of a secondary school assistant principal as the most impactful professional growth opportunities available to beginning administrators. The findings also provide participant descriptions of the positive and negative aspects of the principal preparation and licensure process. The comprehensive descriptions of the job-embedded experiences and educational experiences may serve to inform the development of the clinical internship requirements of principal licensure programs and provide experienced principals guidance in the mentorship of entry year assistant principals. [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.]