Adolescent depression is a prevalent and debilitating disorder that is associated with social and academic impairment, suicidality, comorbid psychiatric disorders, and high-risk behaviors (Horowitz, Garber, Ciesla, Young, & Mufson, 2007). Yet many adolescents experiencing depressive symptoms do not receive adequate services, and those that do often fail to achieve remission. This inconsistency in access and outcome warrants further investigation of prevention interventions, particularly those that can be delivered in settings where services are more accessible to youth, such as schools. One such intervention is Interpersonal Psychotherapy-Adolescent Skills Training (IPT-AST; Young & Mufson, 2003), a school-based indicated prevention program that has been shown to have significant effects on depression symptoms and overall functioning for adolescents (Young, Mufson, & Davies, 2006; Young, Mufson, & Gallop, 2010). The present study seeks to identify factors that impact intervention efficacy of IPT-AST by using a mixed methods approach. Systematic individual pragmatic case studies were conducted with a response and non-response case from Young et al. (2010), which evaluated the efficacy of IPT-AST in preventing adolescent depression compared with typical school counseling. Qualitative data from audio recordings of clinical evaluations and the group intervention were used in conjunction with quantitative data from self-report measures to examine experiences of the selected individuals during the intervention and throughout the subsequent 18 months. Case study findings suggest that individual factors, including attitude towards change, interpersonal history and functioning, anxiety symptoms, and cognitive style, contributed to discrepancies in intervention outcomes. Results also highlight the importance of establishing group trust and practicing interpersonal skills in a wide range of contexts, the implications of which are discussed for future research and program development. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]