Large socioeconomic and ethnic disparities exist in college admissions. This paper demonstrates that by systematically accounting for the effect of socioeconomic circumstance on pre-college achievement, colleges can substantially reduce these disparities. A conceptual model distinguishes students' realized achievement from their underlying ability (inclusive of effort and motivation) and relates achievement differences to both ability and socioeconomic circumstance. The model shows that an admissions policy that systematically accounts for the relationship between circumstance and achievement can significantly increase the representation of socioeconomically disadvantaged and minority students. Empirical findings using California data confirm this result: socioeconomic circumstance is strongly related to pre-college achievement, and much of the ethnic disparity in achievement, as measured by SAT I scores and high school grade point averages, can be attributed to circumstance. The estimated relationship between circumstance and achievement is used to construct alternative measures of achievement that account for the influence of circumstance. Simulation of admissions policies demonstrates that, by relying on such measures, a college can greatly reduce socioeconomic and ethnic underrepresentation among admitted students. (Contains 4 tables, 4 figures and 22 notes.)