Background: Previous research on the correlates of unintentional school injuries is based on either process or cross-sectional data. This study aims at approaching the causal effects of risk-seeking behavior, mental health problems, physical activity, and exposure to bullying on unintentional injuries in the school environment by relying on longitudinal survey data. Methods: The data comes from a German panel survey, including more than 10,000 students. We estimate fixed-effects regression models that only take into account the variation within participants and are therefore most suitable for establishing causal inferences. Results: We find an increase in risk-seeking behavior on the individual level to yield an increase in students' likelihood to suffer injuries during physical education and on the schoolyard or in the school building. The same holds true for an increase in mental health problems. Finally, students who expand their degree of physical activity in club sports also show a higher risk of unintentional injuries. Conclusions: Interventions aimed at reducing too risky behavior and mental health problems may help prevent unintentional injuries in the school environment. Since students who increase their activities in club sports are also more prone to school injuries, preventive efforts should include this group of adolescents as well.