Research was conducted to determine the relative effects of an internship program on the psychosocial development of high school students. Volunteers for an internship program were recruited from a group of high school juniors and seniors. The selected students were matched with mentors who were perceived as supportive of the internship program; open and free in communication; willing to provide time and personal attention to train and direct interns; and willing to allow interns to make decisions and assist in a professional manner. The psychosocial development of participating students was assessed using two methods. These included pre and post data on personality traits obtained through completion of the Gordon Personal Profile; and review of written logs and interview data obtained from the treatment group. The primary data was analyzed using several statistical procedures. The study also identified: (1) which on-the-job factors were effective contributors to facilitating development in students; and (2) the relationship between factors. The intern/mentor relationship was an important factor in psychosocial behavior development. The results of this study present useful information for educators who are interested in implementing an effective experiential education program for high school students. Intern comments taken from logs and interviews are appended. (DWH)