The purpose of this Action Research study was to investigate and improve teacher retention at Southside Public Schools, an urban public school district in Massachusetts. Participants and data collected in Cycle 1 consisted of an interview with the school district's superintendent, a focus group that included Southside's director of human resources, Southside's human resources generalist, the district's business manager, the district's assistant superintendent, and one school principal. Qualitative action research was used to gather data for this study. Cycle 1 findings identified three root causes for teacher turnover at Southside Public Schools: poor workplace climate, lack of administrative support, and low teacher morale. Based on Cycle 1 findings, a task force was assembled from among the various groups of stakeholders in the district. This task force worked collaboratively to completely revamp the district's new teacher onboarding and mentoring program. After implementing the new teacher onboarding and mentor program for five months, interviews and surveys were conducted to determine the extent to which the implementation of the district's onboarding and mentoring program impacted teachers' feelings about job satisfaction and perceptions of workplace climate. Cycle 2 findings indicated that new teachers benefited from the new teacher onboarding and mentoring program, but experienced teachers who were new to the district saw little value in the program. Additionally, teachers recommended that building-based onboarding and training was largely lacking, and this negatively impacted their ability to perform the day-to-day tasks of their jobs. Findings also indicated that it was the existing workplace culture and level of administrative support that impacted their feelings about job satisfaction and perceptions about workplace climate, and not necessarily the presence of a structured new teacher onboarding and mentoring program. Implications from these findings were used to develop recommendations to the district about its continued implementation of the new teacher onboarding and mentoring program as well as recommendations about how improving the workplace culture and level of administrative support could potentially improve long-term teacher retention, and how the presence of a differentiated, structured new teacher onboarding and mentoring program can contribute to the overall workplace culture and support that school administrators should offer to their staff. [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.]