The purpose of this study was to assess school leadership effectiveness on students' academic achievement in terms of leaders' instructional leadership roles and leadership styles and to see factors affecting their effectiveness in the secondary schools of Jimma Zone. The study employed a descriptive survey research design and quantitative and qualitative research methods. Among 18 weredas in the zone, 4 were selected by simple random sampling technique and all of the (8) secondary schools in those weredas were included as a sample. Data for the study were collected through questionnaires, interviews, and document analyses. Questionnaires were prepared and administered to 86 teachers selected by using simple random sampling techniques and 51 school leaders. All principals were interviewed and the analysis of necessary documents was made in all sample secondary schools. The data collected were analyzed by using percentages, means, and weighted means and an independent sample t-test used by computing the data on SPSS version 16.