By means of a longitudinal design the authors sought to determine the role of students' self-determined motivation in reducing the intention to drop out of high school over time, while taking into account the impact of academic performance and of socioeconomic status. The effects of students' self-efficacy and perceived support from parents and teachers were examined. A total of 426 students of grades 9-13 completed self-report estimates and their official school grades were also taken into consideration. Results showed that the level of self-determined motivation in students, which was directly related to the perception of teachers' autonomy support, was the best predictor of the intention to drop out of school. Self-efficacy had a significant impact both on self-determined motivation and academic performance. (Contains 6 tables and 2 figures.)