This study investigated the comparative capacity of women-only and co-educational colleges to impact on two dimensions of women students' intellectual development: (1) intellectual self-confidence; and (2) critical thinking and problem-solving skills. The study also attempted to isolate the effect of attending women-only colleges from other potentially confounding individual- and institutional-level predictors (e.g., degree aspiration, father's education, minority group status) using a multi-level model technique. Data were from the Cooperative Institutional Research Program (CIRP) and the Higher Education Research Institute. The subset of CIRP data included 2,472 female freshmen attending private four-year colleges in the United States who were surveyed during their freshman and senior years. Data from faculty at 392 colleges and universities focused on faculty characteristics and interaction with students. It was concluded that attending a women-only college did have an effect on intellectual self-confidence but did not make a big difference with regard to self-reported growth in critical thinking and problem-solving skills when the effect of attending a black college was controlled. Seven tables contain statistical data supporting the conclusions. Two appendices contain lists of individual- and institutional level-predictor variables. (Contains 41 references.) (CK)