This study investigated the characteristics of instructional leaders that positively influenced classroom teaching, noting the personal and professional effects of leader-teacher interactions and whether staff development emerged as a primary theme of effective instructional leadership. A group of 809 teachers nationwide provided detailed descriptions of instructional leaders' characteristics that impacted their teaching, the areas of impact and effectiveness of the instructional leaders' actions, and their thoughts about such actions. Results indicated that instructional leaders' characteristics profoundly impacted teachers' classroom behavior, leading to powerful cognitive, affective, and behavioral effects on teachers. Effective instructional leaders frequently provided staff development opportunities that addressed emergent instructional needs. The hallmark of effective staff development was a philosophy of, and support for, lifelong learning about teaching and learning. Staff development, as a key aspect of effective instructional leadership, consistently centered on six elements: the study of teaching and learning; collaboration; coaching; action research; resources; and adult development. Implications for staff developers are presented. (Contains 13 references.) (SM)