<p>This study aimed to investigate student- and school-level variables influencing middle school students’ social and emotional competencies and to verify the mediation effects among these variables. Data were obtained from the Seoul Education Longitudinal Study 2020, and a multilevel path analysis was conducted. The analysis revealed that at the student level, higher problematic smartphone use was associated with decreased exercise, reading, and sleep, and lower levels of social and emotional competencies. Additionally, less exercise and reading were related to lower social and emotional competencies. At the school level, a higher proportion of online classes was associated with better peer relationships and higher social and emotional competencies. In mediation analysis, exercise and reading mediated the relationship between problematic smartphone use and social and emotional competencies at the student level. At the school level, peer relationships mediated the relationship between the proportion of online classes and social and emotional competencies. Based on the results, specific strategies for enhancing middle school students’ social and emotional competencies were discussed.</p>