Three-wave cross-lagged dynamics of teacher–student relationship, screen time, and depression and anxiety across school terms: developmental and sex differences

The peak onset of mental disorders occurs during adolescence; therefore, youth mental health conditions have become a major global public health concern, imposing substantial social and economic burdens. Depression and anxiety exhibit distinct developmental and sex-specific patterns, and prior studies indicate that teacher-student relationships and screen time significantly influence school-aged children's mental health conditions. This study aimed to clarify developmental and sex differences in the school term-by-term relationships among teacher-student relationships, screen time, and depression/anxiety. Participants comprised 12,931 students (3,762 females and 4,529 males in grades 4-6, and 2,103 females and 2,537 males in grades 7-9). Stratified analyses were performed by sex and grade level using a three‑wave cross‑lagged panel model corresponding to the three academic terms. Overall, depression/anxiety predicted more negative evaluations of the teacher-student relationship in the subsequent term. Regarding sex differences, among females, longer screen time in the first term predicted higher depressive/anxiety tendencies in the second term. With respect to grade differences, negative evaluations of the teacher-student relationship in grades 4-6 in males predicted higher depressive/anxiety tendencies in the subsequent term, whereas this predictive path was not significant in grades 7-9. The present findings may help inform support strategies tailored to students' school grade and sex, taking into account differences in mental health outcomes. Additionally, they highlight the importance of the early identification of symptoms of depression and anxiety tendencies and of teacher communication practices that reduce students' negative interpretations.