Unmonitored internet use and depression are difficulties that adolescents experience. Efforts to promote healthy adolescent development tend to focus on reducing these two risk outcomes. Therefore, the purpose of this study was to examine how three important school-related factors (teachers, peers, and academics) affect adolescents' levels of unmonitored internet use and depression. For this study, a cross-sectional data analysis was conducted. The sample included 9297 students who participated in two waves of the China Education Panel Survey (CEPS). Structural equation modeling (SEM) was performed using LISREL 8.80 to analyze the data. Monte Carlo resampling was then performed using R to confirm the significance of the mediating effects. Teacher criticism and negative peers can increase unmonitored internet use and depression in adolescents, while academic stress can exacerbate depression. In contrast, teacher praise and positive peers can reduce those risk outcomes. Academic self-efficacy serves as a key mediator of the impacts of teachers, peers, and academics on adolescents' levels of unmonitored internet use and depression. We advocate that schools should establish a positive school climate, provide teacher feedback training and design physical activity programs to improve academic self-efficacy, thereby reducing the risk of unmonitored internet use and depression among adolescents, effectively preventing possible subsequent internet addiction and promoting the mental health of adolescents.