Compared with admissions test scores, why are high school grades better at predicting college graduation? We argue that success in college requires not only cognitive ability but also self-regulatory competencies that are bette indexed by high school grades. In a national sample of 47,303 students who applied to college for the 2009/2010 academic year, Study 1 affirmed that high school grades out-predicted test scores for 4-year college graduation. In a convenience sample of 1,622 high school seniors in the Class of 2013, Study 2 revealed that the incremental predictive validity of high school grades for college graduation was explained by composite measures of self regulation, whereas the incremental predictive validity of test scores was explained by composite measures of cognitive ability.