The three purposes of this study were (1) to evaluate a paper-pencil test of critical thinking skills using physical science content, (2) to compare the effectiveness of Physical Science Study Committee (PSSC) and non-PSSC physics programs in developing critical thinking skills, and (3) to identify teacher-pupil verbal interaction behaviors that enhance the development of critical thinking skills. Data were obtained by testing approximately 1,000 physics students from 27 high schools with pre- and post-tests of critical-thinking skills. An author-constructed instrument and the Watson-Glaser Test, Form ZM (WGCTA) were used. Thirty physics classes were observed and teacher-pupil verbal interaction recorded using a modification of the Flanders System of Interaction Analysis. Some of the principal conclusions of the study were: (1) little evidence was given to support the belief that either the PSSC or non-PSSC program was more effective; (2) development of critical-thinking skills was shown to be related to the teacher-pupil interaction behaviors that increase a student's potential for actively participating in the teaching-learning process; and (3) a linear relationship did not exist between the mean growth scores on each test and the verbal behavior of each class; there were few significant differences between the verbal interaction behaviors of PSSC and non-PSSC classes. (Author/EB)