Correlations between the California Critical Thinking Skills Test--College Level (CCTST) and student-related factors regarded as indicators of academic ability and success were studied in a series of four experiments investigating whether the CCTST measures improvement in critical thinking (CT) skills. During 1989-90, data were collected on 1,196 college students at California State University (Fullerton), some of whom were enrolled in courses specifically designed to improve CT skills. Instructor-related factors were also evaluated for their impact on CT skill development. Regression models were developed for predicting CCTST results. Relationships between reading ability and native English language ability and the CCTST were also examined. CT skills could be predicted by a combination of verbal Scholastic Aptitude Test (SAT) score, mathematics SAT score, and grade point average. CCTST results correlated positively with reading test scores for vocabulary, comprehension, and total score. Non-native English speakers showed virtually no gains in CT skills from pretest to posttest. Only instructor years of teaching experience and recent experience teaching CT skills were related to CCTST results. No evidence was found to suggest that improvement in CT skills is a natural outgrowth of baccalaureate education; skills improvement did result from courses targeting such skills. Twelve tables provide study data. (SLD)