The purpose of this study was to clarify the effect of high school students’ social skills on their adjustment to school, considering their academic performance and their relationships with friends and teachers as mediators. A questionnaire was distributed to 249 high school students. Social skills regarding friends and teachers, relationships with friends and teachers, academic performance, and adjustment to school were measured. The results of path analysis showed that social skills regarding friends affect adjustment to school, mediated by relationship with friends. The results also showed that social skills regarding teachers affect adjustment to school, mediated by academic performance and relationship with teachers.