One purpose of this study was to compare the incremental effectiveness over high school grade point average (GPA) alone of the American College Testing Program (ACT) assessment, the Scholastic Aptitude Test (SAT), and the California Achievement Tests (CAT) in predicting college freshman GPA. A second purpose was to look at the relative effectiveness of the high school GPA, the ACT, the SAT, and the CAT in predicting college freshman GPA. Data were collected from 1453 college freshman. High school grades predicted college GPA better than the ACT, the SAT, or the CAT. Each of the three tests provided an increase in predictive efficiency of 18.47 percent. The ACT, the SAT, and the CAT all possessed the same ineremental validity. (Author/BW)