Relatively few students in selective colleges come from disadvantaged backgrounds, so the rewards of attending such schools go mainly to those already advantaged from birth. There is substantial variation in those colleges' socioeconomic composition, however. Some selective private institutions proportionately enroll five times as many lower-SES students as others. What drives this variation? Longitudinal analyses presented here suggest that, all other factors being equal, private institutions that are historically embedded in elite status maintain less socioeconomic diversity. Conversely, generous financial-aid efforts and test-optional admissions policies appear to contribute to institutions achieving greater SES diversity. The findings suggest several research and policy implications.