This case study examined the initial implementation of an Early Warning Intervention System (EWIS) across three comprehensive high schools in a large suburban school district in Washington State using both quantitative and qualitative methodologies. The purpose of the study was two-fold: to determine the extent to which the initial application of systematic tracking and prescribed attendance, behavior, and course performance interventions reduced the total number of at-risk indicators for students identified as being off-track for graduation; and to identify practices that support initial EWIS implementation effectiveness. At this early stage of implementation, no statistically significant findings resulted from the quantitative data analysis; however, the qualitative research led to important and informative insights into EWIS implementation effectiveness, including the emergence of several important findings: (a) effective school leadership ensured high implementation fidelity; (b) authentic trust, respectful relationships, and ethical leadership were important cultural components; (c) systematic processes included regular cycles of collegial inquiry and collaboration; (d) a comprehensive approach using data driven decision making helped accurately identify off-track students and safeguarded against the effects of subjectivity; and (e) a multi-tiered system of supports allowed for timely application of individualized interventions for off-track students. The case study findings provided a wide range of evidence indicating both positive and promising effects of initial EWIS implementation including important insights around factors related to implementation effectiveness. [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.]