The Wallace Foundation
The Wallace Foundation is a philanthropy working nationally to answer important questions that, if solved, could help strengthen practices and policies within a field.

Vanderbilt Peabody College
Our mission is to enhance the human conditio​n, with a particular focus on children’s learning and development, through the preparation of teachers and leaders; through cycles of research, implementation, and refinement; through service to families, schools, and communities; and through external engagement with professionals, leaders, and policymakers.

NC State University
The College of Education is a voice of innovation for learning across the lifespan. We prepare professionals who educate and lead. Our inquiry and practice reflect integrity, a commitment to social justice and the value of diversity in a global community.

University of North Carolina at Chapel Hill
The School of Education at the University of North Carolina at Chapel Hill is committed to realizing the transformative power of education, and — in turn — is redefining what it means to educate. Education has the power to break down barriers, lift up individuals, and empower communities to rise and thrive. To that end, we inspire educators to lead; to think creatively, act with passion, and strive toward equity for all.

Urban Institute
The nonprofit Urban Institute is a leading research organization dedicated to developing evidence-based insights that improve people’s lives and strengthen communities. For 50 years, Urban has been the trusted source for rigorous analysis of complex social and economic issues; strategic advice to policymakers, philanthropists, and practitioners; and new, promising ideas that expand opportunities for all. Our work inspires effective decisions that advance fairness and enhance the well-being of people and places.

Suggested Citation

Grissom, Jason A., Anna J. Egalite, and Constance A. Lindsay. 2021. “How Principals Affect Students and Schools: A Systematic Synthesis of Two Decades of Research.” New York: The Wallace Foundation. Available at​


We gratefully acknowledge the contributions of the many individuals who made this report possible. Josh Bleiberg was invaluable in setting up our coding and reference management infrastructure, implementing the literature search, and assisting with study coding. Lara Condon, Daniela Barriga, and Elizabeth Uzzel also provided excellent coding and research assistance. Shirley Xu assisted with compiling the reference list. Alphonse Simon and Grace Luetmer at the Urban Institute assisted with analysis of national datasets. We are also grateful to David Golann from Vanderbilt’s Peabody Library, whose expertise informed our database search protocol.

At the Urban Institute, we thank Wesley Jenkins, Brittney Spinner, and John Wehmann for their graphic design work, David Hinson for expertly editing and producing the report, and Alexandra Tilsley for planning and managing communications and outreach.

Our report benefited greatly from thoughtful, probing feedback from five external reviewers: Elaine Allensworth, Sonya Douglass Horsford, David Liebowitz, Sara Morrison, and Jessica Rigby. Brendan Bartanen and Matthew Kraft also provided helpful feedback and advice on specific components of the report.

We also thank the staff of The Wallace Foundation for their thoughtful feedback and expert guidance throughout this process. We especially appreciated the input of Elizabeth Ty Wilde, Pam Mendels, Lucas Held, and Andy Cole.

Lastly, an unusual but rewarding aspect of our effort on this knowledge synthesis was that we worked alongside two other teams writing their own syntheses on related topics with whom we frequently communicated and conferred: Ellen Goldring, Mollie Rubin, Mariesa Herrmann, Linda Darling-Hammond, Marjorie Wechsler, and Stephanie Levin. We appreciated their insights throughout the research process and their feedback on an earlier draft.


education specialist degree. An advanced professional degree designed to provide focused expertise in education leadership or another area beyond the master’s level.

exclusionary discipline. School disciplinary actions that remove students from their usual educational setting. These actions include in-school suspension, out-of-school suspension, and expulsion.

grey literature. Research produced by organizations that is published outside traditional commercial or academic outlets. Grey literature includes reports, working papers, and technical documents produced by governments, research firms, and other entities that are not published in academic journals though they are often still subject to some form of peer review.

in-school suspension. A form of student discipline that temporarily keeps students in school and engaged in schoolwork but isolates them from other students.

longitudinal data. Data that follow the same units (e.g., schools, principals) over multiple years. Also referred to as panel data.

multiple-measure educator evaluation. A system for rating the performance of an educator, such as a teacher or principal, that combines more than one performance metric. These metrics most often are a rubric-based measure of practice (e.g., classroom observations for teachers, leadership practice ratings for principals) and a measure derived from the achievement of the students the educator serves, such as a test score growth measure.

out-of-school suspension. A form of student discipline that temporarily removes students from school and school activities.

panel data methods. A category of statistical tools that rely on data on the same units repeated over time.

phenomenology. A discipline in philosophy concerned with studying how phenomena are consciously experienced from the first-person point of view.

principal. The head or person with the most authority in a K–12 school. In this report, we distinguish principals from other school leaders, such as assistant principals.

Professional Standards for Educational Leaders (PSEL). A set of 10 standards that were released in 2015 by the National Policy Board for Educational Administration. The earlier version of the PSEL were the Interstate School Leaders Licensure Consortium (ISLLC) Standards. Through professional associations, supporting institutions, and policy, the standards are expected to influence leadership practices and, ultimately, leadership outcomes. Member organizations include the American Association of Colleges for Teacher Education, American Association of School Administrators, Council for the Accreditation of Educator Preparation, Council of Chief State School Officers, National Association of Elementary School Principals, National Association of Secondary School Principals, National Council of Professors of Educational Administration, National School Boards Association, and University Council for Educational Administration.

quasi-experimental designs. A class of research approaches that aim to infer causal relationships in the absence of random assignment by comparing units that receive a treatment with a suitable comparison group, with some strategy for accounting for the process by which units are assigned to a treatment or control group.

standard deviation. A way to measure the width of a distribution. Larger values mean that there is more variation in the values a variable takes on.

value-added measures. Metrics derived from statistical models of student test score growth over time that aim to capture the contribution of a schooling input, such as teachers or principals.


In 1999, The Wallace Foundation’s board of directors decided to make what it called a “big bet” on school leadership. At that time, the principalship was not widely seen as crucial in school improvement. The board found this odd. Leadership is critical in nearly every other sector of society—from business to the military, from religion to higher education. They reasoned education leadership might not be getting the attention it deserved.

Since then, leadership has received more attention as an essential ingredient in efforts to improve schools and student learning. A review the foundation commissioned about what was known about the impact of leadership on student learning contributed to this understanding. Published in 2004, How Leadership Influences Student Learning found that leadership was second only to teaching among in-school factors that affect student learning—with investments in strengthening it likely to be cost-effective. This report (downloaded more than 800,000 times from the Wallace website) helped pave the way for a growing consensus that improving the training and support of principals is worthwhile.

Since then, what we know about school leadership has continued to evolve, with more experience, more research, and new research methods. For that reason, in 2019, Wallace commissioned a new review of the evidence base about the link between leadership and learning. (We also commissioned separate reviews we plan to publish later in 2021 on assistant principals and on the preparation and professional development of principals.)

The findings of this new review, How Principals Affect Students and Schools: A Systematic Synthesis of Two Decades of Research, are striking.

The research team of Jason A. Grissom of Vanderbilt University, Anna J. Egalite of North Carolina State University, and Constance A. Lindsay of the University of North Carolina at Chapel Hill concludes that, based on research since 2000, the impact of an effective principal has likely been understated, with impacts being both greater and broader than previously believed: greater in the impact on student achievement and broader in affecting other important outcomes, including teacher satisfaction and retention (especially among high-performing teachers), student attendance, and reductions in exclusionary discipline.

The conclusions about student achievement are based in part on six studies that rely on longitudinal data that allow researchers to track over time the impact of a given principal as he or she moves to different schools and the impact of different principals on the same school. These panel data, unavailable in 2004, help researchers gain a better grasp of the contributions of effective principals, an inherent challenge given that leadership’s impact on students occurs indirectly through teachers and other school personnel.

Importantly, equity occupies a central and timely place in the team’s recommendations for practice and policy—based on principals’ impact on particular groups of students and on the changing demographics of the nation’s student body, which are not yet reflected in the pool of men and women currently in the principalship.

The report makes other contributions, as well. Synthesizing quantitative and qualitative studies, the researchers identify four principal practices that are linked to effective outcomes, as well as three foundational skills. The four practices, which together provide a rounded portrait of principal activities, are high-leverage instructional activities, building a productive culture and climate, facilitating collaboration and learning communities, and the strategic management of personnel and resources. Identifying these practices and skills was important, as they allow us to not only better specify the impact of an effective principal but to know what he or she does to be effective. These insights can, in turn, help make efforts to strengthen leader preparation, training, and support more feasible and effective.

Research evidence is not a silver bullet. Its use, as the scholar Sandra Nutley reminds us, is a varied and complex phenomenon. But there is no doubt it can help us better understand problems and develop potential solutions. Systematic syntheses like this one—using a careful and transparent set of criteria to identify which research to include—can offer particularly robust assessments of the state of knowledge at a given time.

Leaders do not create value directly. They deliver results indirectly, by enabling others to achieve more. It is normally impossible to separate the contributions of the leader and the team members. This suggests that, rather than thinking in terms of either/or, we need a balance of investments in developing great principals and great teachers. In that spirit, we hope this report will be helpful to practitioners, policymakers, and others who are working to improve equitable outcomes for more young people.

Will Miller, President
Will Miller
President, The Wallace Foundation

Executive Summary

Over the past two decades, the policy landscape and the research landscape of school leadership have experienced major shifts. High-stakes accountability, multiple-measure teacher evaluation systems, heightened policy attention to educational equity, and other changes have altered expectations for what leaders need to know, how they spend their time, and the outcomes—both what and for whom—they pursue. In the world of school leadership research, new datasets and methodological advances have opened up new possibilities for measuring what leaders know and do. Longitudinal datasets that track large numbers of schools and principals over time allow researchers to better establish and understand the causal chains that link leadership to student learning and other outcomes, such as by examining how a school’s performance changes when a new principal takes the helm.

This report summarizes what researchers have learned about the connection between school leadership and student achievement and other outcomes in the United States since 2000, picking up roughly where Leithwood and coauthors (2004) left off in their influential Wallace Foundation–commissioned school leadership research review. That report famously concluded that “leadership is second only to classroom instruction among all school-related factors that contribute to what students learn at school” (Leithwood et al. 2004, 5), helping the field understand the importance of school leaders and successful leadership. But the principalship Leithwood and colleagues considered is different from the one we examine, as is the research base from which they could draw. In this report, we revisit, question, and extend these earlier conclusions to provide new direction for practice, policy, and research in school leadership.

We ask three main questions. First, who are public school principals, and how have their characteristics changed over the past two decades? Second, how much do principals contribute to student achievement and other school outcomes? Finally, what drives principals’ contributions? That is, what are effective principals’ characteristics, skills, and behaviors?

How Has the Principalship Changed?

To answer the first question, we first survey the shifting landscape of the principalship over the past few decades, documenting evolutions in federal, state, and local policy (e.g., test-based accountability, increased emphases on engagement with instruction) that have changed the principal’s role. We then analyze nationally representative data collected primarily by the National Center for Education Statistics at the US Department of Education since the 1987–88 school year. We document three key changes: (1) the principalship has become markedly more female, (2) principals’ level of experience has fallen on average and especially in high-need schools, and (3) despite dramatic changes in the racial and ethnic composition of students, racial and ethnic diversity in school leadership has moved only slightly, creating growing racial and ethnic gaps between principals and the students they serve (figure ES.1). Despite their growing presence in public elementary and secondary classrooms, Hispanic and Black students experience the largest principal representation gap. In comparison to their white peers, students of color are less likely to encounter a principal who shares their ethnicity.

Gaps in Principal Representation for Black and Hispanic Students
How Principals Affect Students and Schools FIGURE ES.1
Source: Authors’ calculations from the Schools and Staffing Survey/National Teacher and Principal Survey and the Common Core of Data.
Note: The y-axis shows the share of principals and students in each racial or ethnic group.

Answers to the second and third questions draw on a systematic review of high-quality studies connecting school leaders to student and teacher outcomes. We conducted a systematic search of empirical research studies and “grey literature” sources that yielded more than 4,800 studies. Applying criteria to screen for relevance and rigor, we winnowed this set to 395 studies employing quantitative and qualitative methods, which we full-text coded. After further assessment of the methods, appropriateness of conclusions to those methods, and relevance from this coding, we ultimately synthesized 219 studies.

The Size of Principal Effects

School leadership matters for a host of important school outcomes, including student achievement (as measured by standardized tests), but gauging the size of this impact requires careful analysis. To quantify how much principals contribute to student achievement and other outcomes, we focus on the subset of six rigorous studies that applied panel data methods (i.e., statistical methods for making plausibly causal inferences using data that follow the same schools and principals over multiple years) to measure such effects. Across six studies of data from more than 22,000 principals in four states and two urban school districts, principals matter substantially. We find that a 1 standard deviation increase in principal effectiveness increases the typical student’s achievement by 0.13 standard deviations in math and 0.09 standard deviations in reading. To translate this result, we estimate that the impact of replacing a below-average elementary school principal (i.e., one at the 25th percentile of effectiveness) with an above-average principal (i.e., at the 75th percentile) would result in an additional 2.9 months of math learning and 2.7 months of reading learning each year for students in that school. Effects of this replacement in math would be larger than more than two-thirds of educational interventions compiled in a recent review, and the effects in reading would be larger than about half of interventions (Kraft 2020).

To put the magnitude of these impacts in context, we can compare them with estimates of teacher impacts, as measured by studies employing similar methods (Hanushek and Rivkin 2010). This comparison shows that the impact of having an effective principal on student achievement is nearly as large as the effect of having a similarly effective teacher (or, more precisely, the effect on student achievement of a principal at, say, the 75th percentile of the distribution of principal effectiveness is nearly as large as that of a teacher at the 75th percentile of the teacher effectiveness distribution).

​ ​ Across six rigorous studies estimating principals’ effects using panel data, principals’ contributions to student achievement were nearly as large as the average effects of teachers identified in similar studies. Principals’ effects, however, are larger in scope because they are averaged over all students in a school, rather than a classroom.

Of course, this comparison of principal impacts to teacher impacts is not an “apples-to-apples” one because principals’ effects on students come largely through their effects on teachers, including how principals hire, retain, develop, and encourage teachers and create appropriate conditions for teaching and learning. For an individual student, exposure to strong teaching is paramount; a student learns more in a school with an effective principal in part because the principal makes it more likely the student gets that exposure. For a school as a whole, however, the effectiveness of the principal is more important than the effectiveness of a single teacher. Principals affect all 483 students in the typical elementary school, whereas teachers affect 21 students in the average elementary school classroom. Given the scope of principal effects, we conclude that Leithwood and coauthors’ (2004) judgment about school leadership being among the most important school-related factors that contribute to student learning holds up. In fact, the importance of school principals may not have been stated strongly enough in prior work, particularly from the perspective of state and district leaders and policymakers seeking to move the needle on student achievement. Indeed, it is difficult to envision an investment in K–12 education with a higher ceiling on its potential return than improving school leadership.

Principals really matter. Indeed, it is difficult to envision an investment with a higher ceiling on its potential return than a successful effort to improve principal leadership.

A caveat to this conclusion is that it is based on just six studies, conducted in just a few states and districts, which may not be representative. We need replication of these findings across school levels (these six studies use data primarily from elementary and middle schools) and in different contexts, which can allow for investigation of the conditions under which leader effects are smaller or larger.

Who the principal of a school is matters for outcomes beyond achievement. For example, studies show that some principals are more effective than others at reducing absenteeism and chronic absenteeism. Principals vary in their likelihood of meting out exclusionary discipline (e.g., suspensions). Some are more successful at retaining teachers, including more effective teachers. Moreover, we find that supervisor and teacher ratings of the effectiveness of principals’ practices can predict student achievement growth and other outcomes. This finding suggests that the overall impact of an effective principal can be linked to observable behaviors. That is, how principals approach school leadership directly affects schools’ outcomes.

What Drives Principals’ Contributions?

These observations motivate our investigation of drivers of principals’ impacts on their schools. From the large, diverse body of research we synthesize, which includes both quantitative and qualitative studies, we identify three overlapping realms of skills and expertise that school leaders need to be successful: instruction, people, and the organization. We then describe how these skills and expertise manifest in four classes of behaviors that the best-available research suggests produce positive school outcomes. These behaviors fall under the following categories:

  • Engaging in instructionally focused interactions with teachers. Forms of engagement with teachers that center on instructional practice, such as teacher evaluation, instructional coaching, and the establishment of a data-driven, school-wide instructional program to facilitate such interactions
  • Building a productive school climate. Practices that encourage a school environment marked by trust, efficacy, teamwork, engagement with data, organizational learning, and continuous improvement.
  • Facilitating productive collaboration and professional learning communities. Strategies that promote teachers working together authentically with systems of support to improve their practice and enhance student learning.
  • Managing personnel and resources strategically. Processes around strategic staffing and allocation of other resources.

Principal Skills and Behaviors to Improve School Outcomes
How Principals Affect Students and Schools - FIGURE ES.2

From an equity perspective, we find that principals can have important impacts on key populations, including low-income students and students and teachers of color. These impacts can occur through direct channels (e.g., by how they manage student disciplinary actions) or through indirect channels (e.g., by working with teachers to implement culturally responsive teaching practices, by hiring greater numbers of teachers of color who are influential for students of color). Principals of color may be high-leverage actors in this regard, as they appear especially likely to have positive impacts on both students of color and teachers of color. We draw upon the growing, largely qualitative literature on leadership for equity to illuminate the approaches and strategies equity-focused principals use to affect schools serving historically marginalized student populations.

An additional finding is that principal turnover tends to negatively affect not just student achievement but other outcomes, such as teacher retention and school climate. Principal turnover is higher in schools serving larger proportions of low-income students, low-achieving students, and students of color, suggesting that principal turnover often may reinforce existing inequities among schools. Yet we also uncover evidence that not all principal turnover has negative effects on schools. In cases where districts replace an ineffective principal with a more effective one, impacts may even be positive, though this case does not appear to be typical.

Implications for Policymakers, Practitioners, and Researchers

We conclude with implications of our findings. Foremost, our results on the importance of principals’ effects suggest the need for renewed attention to strategies for cultivating, selecting, preparing, and supporting a high-quality principal workforce. The payoffs to successful strategies appear very large for student learning and for other important outcomes, such as student attendance and teacher turnover. Preservice preparation programs, pipeline initiatives, and in-service learning opportunities can have more positive impacts by focusing on high-leverage practice areas, such as instructionally focused interactions with teachers (e.g., feedback, coaching), building strong relationships and collaborative cultures, and strategic personnel management (e.g., hiring, placing, and retaining effective teachers). The evidence also argues for continued reorientation of the work of school principals toward educational equity and for school districts to prioritize the needs of increasingly diverse student backgrounds, both in hiring and retaining effective leaders for high-need schools and in ensuring that leaders from diverse backgrounds have equitable access to principal roles. On this last point, the benefits of principal racial and ethnic diversity suggest the need for new policies and initiatives aimed at increasing the number of principals of color.

Lastly, we highlight broad concerns about the state of research on school principals. Although this research asks many important questions, our evidence review suggests that studies of school principals too often are marked by methodological and reporting limitations that undermine their conclusions. This review argues for major investment in data collection and capacity building around high-quality research practices and methods if the field is to provide clear, systematic direction for leadership policy and practice.

Summary of Key Findings

In sum, we found the following:

  1. Effective principals are at least as important for student achievement as previous reports have concluded—and in fact, their importance may not have been stated strongly enough.
  2. Principals have substantively important effects that extend beyond student achievement.
  3. Effective principals orient their practice toward instructionally focused interactions with teachers, building a productive school climate, facilitating collaboration and professional learning communities, and strategic personnel and resource management processes.
  4. Principals must develop an equity lens, particularly as they are called on to meet the needs of growing numbers of marginalized students.
  5. Effective principals are not equitably distributed across schools.
  6. Principals are becoming more racially and ethnically diverse, but representation gaps with students are growing, which is concerning, given the payoffs to principal diversity.
  7. Research on school principals is highly variable, and the field requires new investment in a rigorous, cohesive body of research.