School Leadership and Principal Effectiveness: What Research Shows About Impact

School principals are frequently cited as the second most important in-school factor in student achievement after classroom teachers, and research on school leadership has grown substantially as a result. Studies using administrative data, randomized designs, and observational methods have worked to identify what distinguishes effective principals from ineffective ones, how leadership affects student and teacher outcomes, and what preparation and professional development experiences produce strong school leaders. The challenge of studying principal effectiveness is similar to the challenge of studying teacher effectiveness: attributing student outcomes to a specific leader requires isolating the leader's contribution from prior school conditions, student population characteristics, and teacher quality. Research using value-added methods, which track student growth over time and compare it to expected growth given student characteristics, finds substantial variation in principal effectiveness. Studies in New York City and elsewhere find that replacing a principal in the bottom quartile of effectiveness with an average principal produces gains comparable to replacing a teacher in the bottom quartile with an average teacher. Instructional leadership, meaning principals' involvement in curriculum decisions, classroom observation, teacher feedback, and professional learning, is consistently associated with student achievement gains in research. Principals who spend more time in classrooms, who provide specific and actionable feedback to teachers, and who build teacher capacity through professional development show better outcomes than those who focus primarily on administrative and managerial tasks. This finding has influenced principal preparation programs, which increasingly emphasize instructional leadership competencies alongside operational management skills. Building a positive school climate is another domain of principal influence with documented research support. Research on school climate, including measures of student safety, teacher working conditions, and community engagement, finds strong associations with student outcomes and teacher retention. Principals who establish clear expectations, respond consistently to behavioral issues, cultivate trust among faculty, and create structures for family engagement produce school environments that support learning. Principal behavior during the first year of leadership appears particularly important in establishing the norms and culture that persist over time. Principal turnover is a significant concern given the documented effects of principal effectiveness. Research finds that effective principals are disproportionately likely to leave high-poverty schools for more advantaged settings, contributing to the inequitable distribution of school leadership quality. Strategies to retain effective principals in high-need schools, including leadership bonuses, reduced reporting burden, and increased autonomy, have been implemented in some districts, with limited rigorous evaluation. Principal preparation programs have been subject to growing scrutiny and redesign. Research comparing graduates of different preparation programs finds variation in their effectiveness as new principals, suggesting that program content and design matter. Programs that emphasize clinical experience in real school settings, mentorship from experienced principals, and sustained support through early career leadership years produce graduates who perform better on average than programs that rely primarily on coursework. Several states have revised principal certification requirements to mandate stronger clinical components. District support for principals is a moderating factor in leadership effectiveness that research has examined. Principals who receive high-quality coaching, have access to useful data on student and school performance, and are given autonomy to make staffing and programmatic decisions outperform those who are constrained by bureaucratic requirements or who lack support. The relationship between the district and the principal, like the relationship between the principal and the teacher, is a leverage point for improving educational outcomes at scale.