Purpose: A common strategy used in school improvement efforts is a mandated process of formal planning, yet little is known about the quality of plans or the relationship between plan quality and implementation. This mixed-methods article investigates plan quality, factors associated with plan quality, and the relationship between plan quality and implementation, drawing on the first 3 years of a Los Angeles Unified School District school improvement initiative that relied on formal school planning. Research Design: Our research team rated all 206 school plans submitted to the district in the first 3 years of the initiative and drew on surveys of applicant teams and principals implementing the plans. We use these data in descriptive analyses to explore relationships between plan quality and various inputs and outcomes. We also utilized school- and system-level qualitative data to contextualize and explain our findings. Findings: We find that, although average plan quality was relatively low throughout the reform, quality increased during the first phase of the initiative but decreased in the second phase. The two critical elements of the reform intended to drive plan quality, competition and technical support, were negatively or not associated with higher quality plans. However, we find positive relationships between plan quality and reported implementation outcomes in the first phase of the reform, but not in the second. Conclusions: We explore possible explanations for these patterns using qualitative case study and interview data. In the conclusion of the article, we discuss the implications for future school improvement initiatives and research.