Guided by a synthesis of human resource theory as well as teacher effectiveness and school improvement research and policy, this study aimed to better understand school administrators' responses to an externally imposed teacher quality measure (teacher-evaluation) and the extent that this measure influenced the school administrators' leadership work in school improvement. This mixed-method study was conducted in two phases in a large, unit district in Illinois. The first phase utilized a cross-sectional questionnaire with 66 school administrators, which tested their work in implementing the district's new teacher-evaluation process and school administrators' leadership work in school improvement. Phase 2 utilized the interviews of nine purposefully selected school administrators through extreme case and homogenous sampling to further clarify Phase 1 issues of interest. District teacher-evaluation documents were reviewed and utilized to enhance understanding of school administrators' work. Due to the current national discourse regarding teacher-evaluation as a key measure for determining teacher effectiveness and student-learning, the examination of school administrators' work in teacher-evaluation and its influence on school improvement leadership practices is a critical area of study with limited research. This study found a moderate relationship between school administrators' overall school improvement priorities and work on teacher-evaluation, with school administrators' support for change and school administrator-teacher trust having the strongest relationship to teacher-evaluation. These findings were further clarified through three themes and 11 aligned sub-themes regarding school administrators' need to understand evolving priorities at the local level for measuring teaching effectiveness, as well as their changing roles and responsibilities in teacher-evaluation and school improvement. An unanticipated finding that emerged from this study was the variance in foundational relationships among school administrators and teachers, central office administration, and union leadership, and the influence these relationships had upon school administrators' work in teacher-evaluation and school improvement. [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.]