Developed from research on successful school turnaround initiatives that highlight the best practices of school leaders (Elmore, 2004; Leithwood et al., 2010), the Diagnostic Tool for School and District Effectiveness (DTSDE) was introduced by the New York State Education Department (NYSED) as a mandated component of the accountability and improvement processes for turning around underachieving schools were that labeled as Focus Schools or Priority Schools (NYSED, 2012). The DTSDE process has evolved since its inception in 2012, however there is a lack of research exploring the impact of the DTSDE on the long-term leadership actions and behaviors of the school principal that sustain a process of continuous improvement. The purpose of this qualitative comparative case study was to explore the role of principal leadership in advancing the school improvement process by examining the actions and behaviors of principals in four former Focus public secondary schools in New York State. Using the four components of Fullan and Quinn's (2016) Coherence Framework, three research questions studied the school principal's actions and behaviors before, during, and after viii the Focus designation to determine if the structure of the DTSDE sufficiently influenced the school leader's actions and behaviors to sustain a culture of continuous improvement after the Focus designation. Data were gathered through interviews with principals, teachers, and districtlevel leaders. Key findings showed that school leaders were not purposefully promoting a culture of continuous improvement prior to the Focus designation. Participation in the DTSDE process, throughout the Focus designation, led to an increase in the actions and behaviors that are known to support continuous improvement, however the DTSDE did not advance the long-term actions and behaviors of the majority of the principals to the extent described in the Coherence Framework (Fullan & Quinn, 2016) after the conclusion of the Focus designation. Analysis of the data suggested that the DTSDE was effective in advancing the leadership actions and behaviors after the Focus designation in only one out of four cases studied. Several conclusions were identified from the findings including: 1) There was a lack of evidence to support the use of a research-based leadership framework model for continuous improvement, with an embedded data-driven system, prior to the Focus designation; 2) The DTSDE process served as a mechanism for school leaders to begin the process of developing a data-driven culture for continuous improvement during the Focus designation; and 3) There was a lack of evidence to support that the DTSDE process advanced the sustained use of a researchbased leadership framework model for continuous improvement, with an embedded data-driven system, after the Focus designation.