This study examined how three dimensions of college students' experiences affect critical thinking skills: (1) curricular exposure, (2) formal classroom and instructional experiences, and (3) out-of-class experiences. The study used a 1-year, longitudinal, panel study design using data collected as part of a pilot study for a national, longitudinal investigation of factors influencing learning, cognitive development, and orientations toward learning in college. The survey randomly selected 600 students from a population of about 4,500 freshmen students at a large, urban, commuter, research university in Fall 1991. Of these, 327 (54.5%) participated and 210 (64.2%) of these also participated in the follow-up component in Spring 1992. The initial survey used the Collegiate Assessment of Academic Proficiency and also gathered demographic, family, and educational background information. The follow-up instruments included the College Student Experiences Questionnaire. Results indicated that college experiences gave a 6 to 17 percent increase in critical thinking skills, that both class-related and out-of-class experiences made positive, significant contributions to critical thinking scores, and that the number of hours students spent studying and the number of non-assigned books read were positively related to gains in critical thinking. (Contains 46 references.) (JB)