Three empirical dimensions of curriculum structure are presented in this study of the differences among subject areas in student perception of cognitive and affective classroom processes. Class Activities Questionnaire items were used to obtain data from 121 Illinois classes in science, mathematics, social studies, and language arts for grades 6-12. Discriminant analysis reveals the dimensions to be (1) interpreting versus analyzing in contrast to language arts versus mathematics; (2) synthesizing versus knowing in contrast to language arts and mathematics versus social studies and science; and (3) exploring versus evaluating in contrast to science versus social studies. It appears that these school subjects place distinctly different demands on students. (Author)