Purpose: The purpose of this paper is to test the effects of nine district characteristics on student achievement, explored the conditions that mediated the effects of such characteristics and contributed to understandings about the role school-level leaders play in district efforts to improve achievement. Design/methodology/approach: Data for the study were provided by the responses of 2,324 school and district leaders in 45 school districts to two surveys. Student achievement evidence was provided by multi-grade provincial measures of math and language achievement. The analysis of these data included calculation of descriptive statistics, confirmatory factor analysis and regression mediation analysis. Findings: Seven of nine district characteristics contributed significantly to student achievement and three conditions served as especially powerful mediators of such district effects. The same three conditions, as well as others, acted as significant mediators of school-level leader effects on achievement, as well. Practical implications: District characteristics tested in the study provide a powerful framework for guiding the district improvement work of senior educational leaders. The organizational improvement efforts of both district and school leaders would be substantially enhanced by a better understanding of how to diagnose and improve the status of those conditions acting as significant mediators of the effects of both district and school leadership on student achievement. Originality/value: This is one of a very few large-scale quantitative studies examining the extent to which characteristics frequently identified by district effectiveness research explain variation in student learning. It is also one of the very few studies identifying classroom, school and family variables that mediate district effects on such learning. The study also adds to a growing body of evidence about variables which mediate school leaders' effects on such learning.