Although there has been a sizable growth spurt in empirical studies of shared leadership over the past decade, the bulk of this research has been descriptive. Relatively few published studies have investigated the impact of shared leadership on school improvement, and even fewer have studied effects on student learning. This longitudinal study examines the effects of collaborative leadership on school improvement and student reading achievement in 192 elementary schools in one state in the USA over a 4-year period. Using latent change analysis, the research found significant direct effects of collaborative leadership on change in the schools' academic capacity and indirect effects on rates of growth in student reading achievement. In addition, the study identified three different growth trajectories among schools, each characterized by variations in associated school improvement processes. The study supports a perspective on leadership for learning that aims at building the academic capacity of schools as a means of improving student learning outcomes. (Contains 3 tables, 3 figures and 6 notes.)