This article seeks to explain the ways in which leadership makes a difference to the quality of instruction in US schools by reviewing research published since 2000. The review of research is presented in three major sections, organised according to the methodology used in each study. The first section looks into quantitative studies that probe the structural relationships among members and activities related to teaching and learning. Primarily drawing on surveys completed by school stakeholders, these studies uncover patterns of influence using advanced statistical methods. The second section summarises findings from qualitative case study research, which provide specific examples of conditions that support the leadership patterns previously identified. The final section offers further explanations of how these patterns of influence operate by examining the alignment of formal and social components of interactions through network methodology.