The purpose of this study was to propose and test a motivational model of high school dropout. The model posits that teachers, parents, and the school administration's behaviors towards students influence students' perceptions of competence and autonomy. The less autonomy supportive the social agents' behaviors are, the less positive the students' perceptions of competence and autonomy. In turn, the less positive students' perceptions are, the lower their level of self-determined school motivation are. Finally, low levels of self-determined motivation lead students to develop intentions to drop out of high school, which are later implemented, leading to actual dropout behavior. This model was tested with high school students (N = 4,537) by means of a prospective design. Results from analyses of variance and a structural equation modeling analysis (with LISREL) were found to support the model for all participants and for each gender separately.