Four experiments were conducted to determine if the California Critical Thinking Skills Test--College Level (CCTST) measured the growth in critical thinking (CT) skills achieved by college students completing approved CT courses. The experiments, conducted at California State University (Fullerton) involved 1,169 college students in 5 courses with 20 instructors. The theoretical construct for the CCTST is the consensus conceptualization of CT reached by a panel of 46 experts participating in a Delphi research project of the American Philosophical Association during 1987-89. Experiment 1, comparing pretest and posttest scores of students enrolled in CT courses, demonstrated significant growth in CT scores. As a control, the second experiment related CCTST scores of two independent groups enrolled in introduction to psychology courses. The null hypothesis was retained. In the third experiment, using paired pretest/posttest scores, the CCTST measured the growth in CT skills assumed to have occurred as a result of one semester of approved CT instruction. The fourth experiment retained the null hypothesis for the control group using paired pretest/posttest scores. Data are summarized in one table. (SLD)