The purpose of this paper was to examine trends in major components of career development across grades 8 to 12. A set of 11 scales was used to assess various components of career development. Both cognitive and behavioral components of career development were assessed. Longitudinal data from four high schools were analyzed in conjunction with cross-sectional data from three nationally representative samples. The study design controlled for the effects of systematic career guidance programs, career education programs, and related interventions on the normal rate of career development. Four high schools representing various geographic locations and community sizes were involved in the longitudinal phase of the study. All schools administered the Assessment of Career Development to ninth graders in the spring of 1973. These students were retested at a one-year and/or three-year interval. The study results appear to have important implications for practicing counselors. Although career-related knowledge and involvement both exhibit growth during the adolescent years, the data indicate that they are relatively independent components of career development. So counselors need to emphasize both knowledge and behavioral aspects in their day-to-day individual and programmatic efforts to improve upon students' normal, minimal career development growth. (Author)