The Norwegian sport school system offers a method for helping young dual-career athletes achieve their best both in academia and sports. However, there remains a concern that pursuing dual careers at a young age may leave some student-athletes vulnerable to poor mental health outcomes. The aim of this study was to investigate the association between gender, grade, and sport type and problematic scores on school burn-out, sport burn-out, self-esteem and psychological distress in student-athletes within a sample of Norwegian lower secondary schools. A sample of 642 student-athletes (ages 12-14) in grades 8-10 across 8 Norwegian lower secondary sport schools completed questionnaires on burn-out, self-esteem and psychological distress at the beginning of the school year. Females were more likely to report high levels of sport-related burn-out and psychological distress, and low self-esteem; older student-athletes were more likely to report severe school-related and sport-related burn-out; and individual sport student-athletes were more likely to report high levels of psychological distress. Lower secondary sport schools in Norway may seek to be aware of the challenges facing student-athletes for informed practical steps to protect their mental health and maximise their outcomes as school students and athletes.