This study explores the connections between aspects of the school environment and emotional problems among boys and girls. The sample comprised 2,120 adolescents aged 17 and 18 years, in 129 school classes from 13 upper secondary schools in Trøndelag county, Norway. The response rate was 79%. The girls reported more emotional problems than the boys. Variations in perceptions of emotional problems between schools and classes is an under-researched topic. Multilevel models revealed a substantial class-level effect regarding emotional problems and a smaller school-level effect. Emotional problems varied between classes because of the class composition (share of boys and girls) and the class context. Contextual factors relevant to emotional problems were peer support, teacher support, and that emotional problems could 'spread' in a class. Relations between emotional problems and peer support, teacher support, and parental support were stronger for girls than boys. The study emphasizes the importance of the classroom environment, and it suggests that fostering strong relationships between adolescents and teachers, as well as addressing emotional issues among adolescents, can have a positive impact on emotional well-being. An important topic for future studies is whether the inclusion of the health and life skills theme improves mental health support in schools.