Given the number of negative influences on youth and the resultant potential for adverse outcomes, it is crucial to support their positive development. Leadership training programs can promote the development of adaptive intrapersonal qualities. The Teen Leadership Breakthrough (TLB) program claims to create sustainable changes in youth using experiential activities, direct instruction, and feedback to teach leadership skills. This study evaluated the TLB program's efficacy in developing intrapersonal skills in 10th- and 11th-grade students. Participants were randomly assigned to a control or treatment group. Assessment of emotional intelligence and self-concept occurred prior to, immediately after, 6 weeks and 6 months following the intervention. Results indicated that the TLB program created sustainable changes emotional intelligence and self-concept. Although these results are encouraging, further research is needed to investigate the effectiveness of the TLB program in broader demographic groups and to examine different outcomes. (Contains 3 tables.)