This study analyzed skills, strategies, and theories that new middle school principals used to be successful during their transition period (the first 90 days) in turnaround schools. Based on research on transitions, three research questions guided the study: 1. Do middle school principals in a turnaround school situation find the transition period (first 90 days) to be important? 2. What strategies and conceptual frameworks (leadership theories) were useful to new principals during the transition period (first 90 days) in a turnaround school? 3. Did any programs, formal or informal, prepare new principals for success during the transition period (first 90 days) in a turnaround school? The mixed-methods study (using both qualitative and quantitative research elements) was completed by a cohort of 10 researchers. Each cohort case study focused on a new middle school principal in southern California. The cohort members analyzed the leadership strategies that these principals utilized during the first 90 days. Cross-case analysis revealed the following results: 1. New principals must to gain "early wins" during the first 90 days in order to gain credibility and trust of the stakeholders and to create momentum. 2. New principals must gain the trust of and develop relationships with stakeholders of the organization within the first 90 days. 3. The first 90 days constitute a critical period for the new middle school principal, during which the new leader accelerates to the "break-even" point. 4. The contemporary university and preparation programs do not adequately prepare principals to assume the new roles and responsibilities. New principals are not adequately prepared for the demanding responsibilities of the position. It was concluded that formal and informal training programs are needed to provide principals with the practical skills, knowledge, and strategies to assume the demanding and challenging responsibilities of turnaround middle school. These programs can achieve these goals by establishing appropriate mentorship programs. They can also implement fieldwork that provides on-site practical experience. [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/en-US/products/dissertations/individuals.shtml.]