Achievement goal theory is an important theoretical framework for understanding achievement motivation. In previous studies, a mastery orientation has been shown to be related to students' interest, while a performance orientation has been found to be predictive of academic performance outcomes such as course grades. In this study, the two mastery sub-scores from the Multiple Goals Theory Measure (MGTM) of academic motivation, which was developed specifically from achievement goal theory, was found to be predictive of college grades for a sample of 257 undergraduates at a public university in the north-eastern United States. Additionally, the results support a trichotomous model of achievement orientations comprising mastery approach, performance approach, and avoidance. The MGTM appears to hold promise as a diagnostic tool, but additional research is required on its resistance to faking and other threats to validity. (Contains 4 tables.)