The subjects (numerically unspecified) were primarily full-time students, with a significant number being full-time law enforcement officers. Three classes enrolled in other courses were used as a control group. Both groups were given various tests to measure attitudes toward the criminal justice system, and the criminal justice students were tested on knowledge of the system. The tests were repeated at the end of the 10-week quarter during which the class was taught. The experiment was conducted over two university quarters. All students had relatively positive pretest attitudes toward the criminal justice system. In the course of the program, attitudes of students enrolled in the class became more positive toward the concepts of law enforcement and toward law enforcement officers. Police officers taking the course registered a positive gain in attitude toward their role and toward other elements in the criminal justice system. There were high correlations between favorable attitudes toward the criminal justice system and friendships or relationships with persons working within it as well as between attitudes and past experiences with the police. Older subjects were more likely to rate criminal justice concepts higher than younger ones. The characteristics of the instructor teaching the course were important in developing attitudinal changes. Training programs for police officers should include a comprehensive treatment of the criminal justice system as part of the curriculum. Extensive tabular data, eight references, and a nine-item bibliography are included. Appendixes include a copy of the course outline, correspondence, a student opinion survey form, a student characteristic survey form, semantic differential scales, and a criminal justice system knowledge test copy. (Author abstract modified)