An assessment study was conducted to test the effectiveness of the Career Planning Support System (CPSS) materials that were developed to provide systematic program planning for high school career development programs. In 1978-79, eighteen high schools in seven states were evaluated using a pretest-posttest, experimental-control group design. Both experimental and control schools were monitored by telephone calls and site visits in addition to pre- and posttests. A group of experts in fields related to career development and practice completed 21-page rating instruments for each participating high school. A score describing each school on each variable was calculated by forming the average over the three or four raters who rated each school. Data were analyzed using analysis of covariance (ANCOVA). Results showed positive growth of career development activities in the experimental schools as opposed to the controls. It was concluded that the gains were of sufficient magnitude to be nontrivial, and that CPSS addresses an important educational need. (Note: the evaluation focused on the process of career development planning and activities, not on effects on students.) (KC)