The purpose of this study was to determine social processes of sex differentiation for undergraduate and graduate students in mathematics and how those processes relate to educational inequity. To gather data relevant to those processes, 168 in-depth interviews were conducted with male and female students majoring in mathematics and with faculty at three Chicago area universities. The strength of the study rests in (1) the focus on females who have "survived" the high school attrition process and who are able mathematicians upon entry into college, (2) the pervasive focus on social processes in which educational experiences are embedded, and (3) the systematic sex-comparative research design. Data analysis was qualitative in nature, and the data are presented in the form of (1) simple distributions of responses suitable for determining overall patterns and (2) an analysis of direct quotes to determine personal meanings. An explanatory schema is presented regarding sex-differentiation which was induced from the data. That schema hinges on processes of self-selection, differential association, sex variation in the specificity of support networks, narrow versus diffuse perceptions of the world, and differences in opportunism and instrumentality. Little evidence of systematic or overt sex discrimination was found in the universities. (Author)