This study is the latest in a series of meta-analyses that Mid-Continent Research for Education and Learning (McREL) has conducted over the past several years to determine the characteristics of effective schools, leaders, and teachers. This most recent meta-analysis examines findings from 27 studies conducted since 1970 that used rigorous, quantitative methods to study the influence of school district leaders on student achievement. Altogether, these studies involved 2,817 districts and the achievement scores of 3.4 million students, resulting in what McREL researchers believe to be the largest-ever quantitative examination of research on superintendents. The following four major findings emerged from the study: (1) District-level leadership matters; (2) Effective superintendents focus their efforts on creating goal-oriented districts; (3) Superintendent tenure is positively correlated with student achievement; and (4) A surprising and perplexing finding of "Defined autonomy." A bibliography of reports used in the meta-analysis is included. (Contains 5 figures.)