The authors examined the differential effects of prior academic achievement, psychosocial, behavioral, demographic, and school context factors on early high school grade point average (GPA) using a prospective study of 4,660 middle-school students from 24 schools. The findings suggest that (a) prior grades and standardized achievement are the strongest predictors of high school GPA and (b) psychosocial and behavioral factors (e.g., motivation, self-regulation, and social control) add incremental validity to the prediction of GPA. When comparing the relative importance of each set of predictors (the dominance analysis technique), the variance accounted for by psychosocial and behavioral factors is comparable to that accounted for by prior grades. These findings highlight the importance of effective risk assessment based on multiple measures (i.e., academic, psychosocial, and behavioral) for the purpose of identifying risk, referring students to intervention, and improving academic success. (Contains 1 figure, 5 tables, and 3 footnotes.)