As part of the Every Student Succeeds Act, the teacher evaluation system includes qualitative and quantitative data to measure teacher quality. Today, school administrators are expected to interpret classroom observation ratings and student growth data to make decisions for instructional improvement. The goal for using an interpretive qualitative research design as the approach for this study was to understand how the school administrators make sense of their experiences of interpreting and using teacher effectiveness data to improve teaching quality. For this study, I described how principals make sense of the teacher effectiveness data, which consists of classroom observation ratings and student growth data, in an effort to build teacher capacity. The purpose of this interpretive qualitative research study is threefold. First, I sought to understand how school administrators interpret teacher effectiveness data. The second purpose of this research study was to understand how school administrators use this data to make decisions. In addition, I explored the types of leadership approaches that school administrators employ to determine how to build teacher capacity. In an effort to understand principal leadership approaches in making campus decisions for instructional improvement, I documented the perspectives, experiences, and challenges encountered in their natural setting while interviewing 10 participants. Due to the widespread impact of COVID-19, the interviewing process was changed from face-to-face to virtual interviews for the safety and protection of all parties involved. Through data analysis of interviews, observations, and reflections, 9 themes emerged from this study and are divided into 4 categories--teacher effectiveness data, measures of teacher practice, measures of student growth, and leadership approaches that were guided by the teacher effectiveness conceptual framework. The themes of staffing and growing teachers, misaligned data, and performance incentive were categorized under teacher effectiveness data. The themes of inconsistent data and primary use of data were categorized under measures of teacher practice. In the measures of student growth data, the themes of inequitable data and supplemental use of data emerged. Ongoing and collective leadership and challenges with building teacher capacity emerged from the leadership approaches category. [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.bibliotheek.ehb.be/en-US/products/dissertations/individuals.shtml.]