There is a growing interest on the role of noncognitive factors such as personality traits and implicit beliefs in accounting for individual differences in academic performance. Autonomy support from primary socializing agents too is an important tool for enhancing student motivation and other learning outcomes. In this study, we tested a model hypothesizing that the broad personality traits of conscientiousness and openness, growth mindset, and perceived teacher and parent autonomy support would be distal predictors of academic performance, with self-determined motivation proximally accounting for performance outcomes. Middle school students (N = 234) completed an online Qualtrics survey. Students' year-end grade point averages for all subjects were used as an indicator of their academic performance. We found that conscientiousness had direct and indirect effects (through autonomous motivation) on academic performance. Openness, growth mindset, and parent autonomy support were indirectly associated with academic performance through their effects on autonomous motivation. The effect of teacher autonomy support on academic performance was mediated by both controlled motivation and autonomous motivation.