This study exploits Seoul’s 2010 high school equalization policy to empirically examine how differences in average academic achievement across schools translate into school effects on individual students. It links the 2005 Korean Education Longitudinal Study (KELS) data with school-level results from the National Assessment of Educational Achievement for Seoul high schools in 2010, and estimates the effect of being randomly assigned to a school with a higher average achievement level. To strengthen the assumption of random assignment within each school district, the analysis clusters geographically adjacent high schools within districts ― thereby comparing students within groups of nearby schools ― while additionally controlling for a wide range of students’ observable socioeconomic background variables.

The results indicate that a significant portion of the achievement gap observed across schools reflects causal school effects. On average, students who attended schools with a higher share of students performing at “proficient or above” showed greater improvements in first-year high school achievement test scores, College Scholastic Ability Test (CSAT) scores, and class comprehension. However, the study finds no statistically significant effects on outcomes beyond academic achievement, such as values formation or non-cognitive abilities, and the achievement gains are concentrated among students who had already exhibited high performance prior to entering high school. These findings suggest that improvements in academic performance do not necessarily extend to broader dimensions of student development, and they also imply that educational investments for students who are already behind in the admissions competition may be relatively insufficient even among high-performing schools.

The study then explores which school characteristics may be associated with the estimated school effects. Among the school-type features available in the data, single-sex status, private school status, and the share of highly educated teachers show significant relationships. Further analyses using survey data from students and teachers reveal clear associations with teacher quality, the school climate experienced by students, and the strict enforcement of school rules. In contrast, no significant relationships are found for characteristics such as the student·teacher ratio, the share of tenured (regular) teachers, or school land area per student. Overall, these results imply that qualitative features―such as teacher capacity and school climate ― may matter more for strengthening a school’s educational effectiveness than quantitative inputs like the number of teachers.

Abstract (ENG)
Preface
Summary (KOR)

Chapter 1. Introduction

Chapter 2. Literature Review

Chapter 3. Methodology
　Section 1. Data
　Section 2. Identification Strategy
　Section 3. Validation and Refinement of the Identification Strategy

Chapter 4. Exploring School Effects on Student Achievement
　Section 1. Effects on Academic Achievement
　Section 2. Effects on Noncognitive Outcomes

Chapter 5. Exploring the Mechanisms of School Effects
　Section 1. School Type
　Section 2. Teacher Competence
　Section 3. School Climate and Culture

Chapter 6. Conclusion

References
Appendix