The late 1990s brought a marked increase in the amount of educational administration research seeking to quantify the influence of leadership on student learning. Questions such as “do principals influence academic achievement?” and “if so, to what degree?” guided much of the work in that era. The field now has a robust knowledge base on which to assert that school leaders do in fact impact student learning. This article provides a brief review of literature attending to the aforementioned questions, as well as a discussion of the clusters of influence through which leadership’s influence occurs. Additionally, we discuss approaches to measuring influence with a focus on evaluation systems.