This report, the fourth in an IERC series on public school principals in Illinois, summarizes recent research on the characteristics associated with principal effectiveness and examines Illinois data on the relationship between principal characteristics, student proficiency, and teacher qualifications. In order to investigate the relationships between principal characteristics, teacher qualifications, and student achievements using Illinois data, we use two-level hierarchical linear growth models to measure the impact of principal characteristics on growth in student proficiency and teacher qualifications over time. In these models, the first level measures within school change over time and the second level measures differences between schools in initial school achievement or teacher qualifications status. Appended are: (1) Statistical Models; (2) Descriptive Statistics for Variables Included in Statistical Models; (3) Results from Model of Student Proficiency; and (4) Results from Model of Teacher Academic Qualifications. (Contains 3 tables and 3 footnotes.)