This comprehensive meta-analysis on teacher career trajectories, consisting of 34 studies of 63 attrition moderators, seeks to understand why teaching attrition occurs, or what factors moderate attrition outcomes. Personal characteristics of teachers and the attributes of teachers' schools are key moderators. The evidence suggests that attrition from teaching is (a) not necessarily 'healthy' turnover, (b) influenced by various personal and professional factors that change across teachers' career paths, (c) more strongly moderated by characteristics of teachers' work conditions than previously noted in the literature, and (d) a problem that can be addressed through policies and initiatives.