Recent studies in Economics have found that the idiosyncratic effect of school leaders may be an important factor in improving student outcomes. The specific channels through which principals affect schools are, with minor exceptions, still largely unexplored in this literature. Employing a unique administrative panel data set from the Victorian public school system, we construct estimates of the idiosyncratic effects of principals on student achievement. We do so using fixed effects techniques and turnover of principals across schools to isolate the effect of principals from the effect of schools themselves. More importantly, through annual detailed staff and parent surveys, we investigate several potential mechanisms through which individual principals may affect student outcomes.