This dissertation was designed to explore the impact of the identified responsibilities of the principal, as an instructional leader, within the professional development model of Reading First. Specifically, the research focused on the principals' use of the Observation and Constructive Feedback Processes as well as five specifically defined Principal Leadership Proficiencies. Three years of longitudinal data from 85 schools throughout Arizona were studied. The exploration of 16 hypotheses was intended to identify definitive proficiencies that supported and/or facilitated teachers' provision of scientifically based reading instruction (SBRI) in Arizona's Reading First classrooms. The tasks of the principal were tested independently and jointly with observation-feedback to explore the existence of a statistically significant relationship with the teachers' use of SBRI. Thirteen of the sixteen hypotheses demonstrated statistical significance at or above the 95% level. The use of each of the principal leadership variables in combination with the Observation-Feedback Processes demonstrated statistically significance influence on the teachers' use of SBRI. The researcher's primary recommendation is that the methods used in this professional development model could serve as an evaluation tool to identify schools in need of intervention and schools attaining exemplary status. This approach has implications for sustainability, funding, and intervention services. [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.]