This study explored how psychosocial features of the schoolwork environment are associated with students’ mental health. Data was drawn from 3699 ninth grade (15 year-old) Swedish students participating in the Health Behaviour in School-Aged Children survey. Using Structural Equation Modelling, perceived school demands, decision control and social support from teachers, classmates and parents were examined in relation to students’ emotional and conduct problems. Higher demands were associated with greater emotional symptoms and conduct problems. Although weaker social support predicted emotional symptoms and conduct problems, the relative influence of teachers, classmates and parents differed. Teacher support was more closely associated with conduct problems, particularly for girls, while classmate support was more strongly related to emotional symptoms. The findings indicate that while excessive school pressure is associated with poorer mental health, social support can assist in optimising adolescents’ emotional health and adaptive behaviour, as well as shaping perceptions of demands.