Boys adjudicated for delinquent behavior and living in a setting guided by behavior modification principles were administered a questionnaire with a semantic differential measure of self-concept several times during their stay (N = 16). A control group of eighth grade boys (N = 82) was given this questionnaire once. As a group, the boys at admission had much more negative feelings about themselves than did the boys in the control group (p < .01). However, when the mean of the pretest group was compared with the mean of the posttest group (which was more positive in self-concept than the control group), the delinquent boys were found to have a much more positive self-concept at the completion of their stay (p < .01). This shift in self-evaluation was concomitant with a shift in how the boys perceived that significant others (mother, friends, and teachers) evaluated them.