The effects of a family's socioeconomic status on psychological differentiation were tested separately, using the Hidden Figures Test, the Hidden Pattern Test, and the Modified This I Believe Test performance of 53 male and 87 female white undergraduates who were widely distributed on socioeconomic status and background demographic characteristics. Contrary to the social class hypothesis, father's socioeconomic status was not related to any of the psychological measures. Instead, the socioeconomic status of the respondent's best friend, the size of the home community (inversely), and being of Northern European ethnic heritage showed more consistent prediction across the three analyses. Social class per se is probably less important for psychological development than are biological endowment and particular environmental interactions of the respondent. The importance of the social status of the respondent's best friend suggests that differentiated individuals tend to self-select complex environments in which to act more often than social-class-related multifaceted environments tend to produce differentiated individuals. (Author)