Principals are understood to be critical actors in improving teaching and learning conditions in schools; however, relatively little is known about the leadership strategies to which principals should dedicate their time and effort to improve outcomes. We review the empirical literature from 51 studies of principal behaviors and student, teacher, and school outcomes and conduct a meta-analysis of these relationships. Our analysis has three central findings: (1) we find direct evidence of the relationship between principal behaviors and student achievement (0.08-0.16 SD), teacher well-being (0.34-0.38 SD), teacher instructional practices (0.35 SD), and school organizational health (0.72-0.81 SD); (2) we highlight the importance of principal behaviors beyond instructional management as potential tools to improve student achievement outcomes; and (3) the preceding findings are based almost entirely on observational studies because the causal evidence base on school leadership behaviors is nonexistent. We argue our findings suggest value in investing in school leadership capacities. We conclude by discussing opportunities to improve the quality of future research examining the relationship between principal behaviors and student, teacher, and school outcomes.