The present study investigated bidirectional associations between teachers' sense of inadequacy and self-efficacy and factors related to them across one academic year. Teachers (N = 52) rated their sense of inadequacy and self-efficacy in fall and spring, and reported the number of students in need of support in spring. The results of cross-lagged path models showed that teachers' sense of inadequacy in fall negatively predicted their subsequent self-efficacy, especially in the dimensions of student engagement and classroom management. In addition, teachers' work experience and number of students with need of support in terms of social and behavioral problems were related to teacher self-efficacy (TSE). Based on these findings, the number of students in need of support in the classroom is a critical factor that influences TSE; therefore, teachers may need support to manage students with needs in terms of social and behavioral problems to maintain their sense of high self-efficacy.