Identifying the best predictors of academic performance is crucial for postsecondary institutions seeking students with the greatest promise. We investigated the relative strength of standardized test scores (ACT), high school GPA, and non-cognitive, college readiness skills in predicting college GPA. College freshmen (505) completed the 108-item Student Readiness Inventory (Le, Casillas, Robbins & Langley, 2005) and reported their high school GPA. We also obtained college GPA for 375 students from college records. In Study 1, MANOVA results showed that students in groups with higher high school GPA or lower ACT reported increased college readiness. In Study 2, regression analyses showed that although ACT scores predicted 13% of the variance in college GPA, high school GPA predicted an additional 11%, and Academic discipline, a non-cognitive factor, predicted an extra 2%. Further, Academic discipline partially mediated the relationship between high school GPA and college GPA. We discuss implications of identifying and assisting "at-risk" students. (Contains 4 tables and 1 figure.)