The purpose of this study was to determine whether or not the implementation of a mandatory uniform policy in urban public high schools improved school performance measures at the building level for rates of attendance, graduation, academic proficiency, and student conduct as measured by rates of suspensions and expulsions. Sixty-four secondary schools serving students in grades 9-12 in Ohio's eight largest cities were included in this study. Four comparisons were used to ascertain if the school uniform policy influenced improvements in school performance measures, employing a time-series quantitative design. These four methods were used to control for other plausible explanations for improvements by grouping schools locally and statewide, and by matching similar schools based on enrollment demographics and administrators' survey responses. Analyses employed ANOVA and t-tests with Cohen's d for small sample size. Through these four comparisons, a pattern emerged that indicated improvement in rates of attendance, graduation, and suspension, but not in academic proficiency or expulsion rates in these schools with uniform policies. It was also determined that schools with uniform policies had higher proportions of economically disadvantaged and minority students than the larger population of urban public high schools. Implementation of a uniform policy in these schools may be effective for improving rates of attendance, graduation, and suspensions. These results may be important considerations for urban public schools seeking alternative means to improve their performance outcomes. Appended are: (1) Letters of Approval; (2) School Data; (3) Communications to Schools; (4) School Improvement Survey; and (5) Survey Data for Matched Schools. (Contains 34 tables.) [Ed.D. Dissertation, Youngstown State University.]