Developmental research in the social-cognitive tradition has provided ample evidence for systematic relations between adolescents' social-cognitive development and mental health problems; both are set within an adolescent's ecology. However, appropriate assessment procedures for school-based prevention reflecting this differential knowledge are largely absent. The aim of this article is to outline the development and application of a new, holistic assessment procedure for youth that includes indicators of adolescents' social-cognitive development and related resiliencies, risks, and relationships. Using quantitative and qualitative data from the ongoing, school-based RALLY prevention program, we illustrate the development and efficiency of this holistic assessment tool within a developmental-ecological framework. This article argues a holistic assessment tool can guide the prevention services to address the individual needs of adolescents and to ideally support their developmental and learning capacity. Finally, the implications for practitioners are discussed.