School‐Based Social Relationships and Adolescent Mental Health: A Multilevel and LASSO ‐Based Analysis

BACKGROUND: This study examined associations between school-based social relationship quality (school belonging, peer support, teacher-student interaction) and mental health outcomes among high school students in Iran, identifying protective and risk factors for depression, anxiety, and stress. METHODS: A cross-sectional survey was conducted in 2024 among 1200 students from 32 public and private high schools in Tehran-Iran. Standardized measures were used to assess school belonging, perceived peer support from friends, teacher-student relationship quality, and symptoms of depression, anxiety, and stress. Data were analyzed in R using multilevel mixed-effects models, quantile regression (50th and 90th percentiles), and LASSO-based variable selection (glmnet). RESULTS: Higher school-based relationship quality was associated with lower depression, anxiety, and stress. Effects were stronger in public schools than private schools: Depression β = -1.727 versus -0.966; Anxiety β = -1.513 versus -0.819; Stress β = -1.601 versus -0.868. Academic stress was the strongest risk factor (β ≈ +1.60), followed by social media use (β ≈ +0.33). Socioeconomic status (SES) showed protective effects (β ≈ -0.72-0.81). Gender and age were minor; quantile regression showed stability. IMPLICATIONS FOR SCHOOL HEALTH POLICY: Strengthening school belonging, peer support, and teacher-student relationships, reducing academic stress, and supporting low-SES students may improve mental health. CONCLUSION: School relationships are key protective factors, with stronger effects in public schools, supporting school-based interventions.