This study compared the effectiveness of ACT[R] Composite score and high school grade point average (HSGPA) for predicting long-term college success. Outcomes included annual progress towards a degree (based on cumulative credit-bearing hours earned), degree completion, and cumulative grade point average (GPA) at 150% of normal time to degree completion (year 6 and year 3 for four- and two-year institutions, respectively). The utility of the individual ACT College Readiness Benchmarks for predicting long-term college success was also evaluated. Data for this study included over 190,000 ACT-tested students who enrolled in college as first-time entering students in fall, 2000 through 2006. Over 100 total two- and four-year institutions were represented. Hierarchical logistic models were used to estimate institution-specific probabilities of college success based on ACT scores and HSGPA. First-year college GPA was also included as a predictor in the path analysis models. Accuracy and success rates were calculated using the distributions of ACT scores and HSGPA for each institution's approximate applicant pool; rates were then summarized across institutions. Direct and indirect effects of ACT score, HSGPA, and first-year academic performance on subsequent college outcomes were also examined. Results were disaggregated by institution type. Both ACT Composite score and HSGPA were effective for predicting long-term college success at both four- and two-year institutions. Across the outcomes, test scores increased prediction accuracy over that for HSGPA alone. ACT scores and HSGPA were primarily indirectly related to subsequent college outcomes (through first-year college GPA). The ACT Benchmarks were also found to be useful for predicting long-term college success, providing further validity evidence for using them as measures of college readiness. (Contains 20 tables, 19 figures and 15 footnotes.)