The undergraduate liberal arts program is assumed to promote sophistication in thinking. At the same time, certain levels of cognitive ability are assumed to be present in students accepted into selective undergraduate colleges. Beginning in the fall of 1991, a long-term research study was undertaken at a small residential liberal arts college that was designed to test both of these assumptions. Some data were collected from each of the 1,7777 students who matriculated in fall 1991, 1992, and 1993. Students were assessed for formal operational ability and intellectual flexibility at the beginning of their freshman year, as sophomore, and finally as seniors. Although it is not possible to differentiate them from changes that might have occurred just because of the passage of time, the findings do suggest that the young adults in this sample did become less concrete and more formal thinkers over their college careers (percent concrete thinkers decreased from 21.8% to 7%). Participants also became less absolute and more evaluative in their approach to problems. (Contains 28 tables and 7 references.) (Author/SLD)