Evidence-based psychotherapy (EBP) proposes the fit between a specific treatment, therapist, patient and mental disorder. At the same time, the generalization of psychotherapy research findings is intended. In this conflict between individualized and standardized treatment the search for specific active components of psychotherapy is essential to improve intervention methods as well as training of therapists. Many manualized treatments for children and adolescents are considered evidence-based, proven by its outcome. However, their active ingredients often remain unclear. The following methods to identify necessary active components for successful treatments are described: classical comparative randomized controlled trials, dismantling studies, add-on studies, meta-analyses, and the multiphase optimization strategy. Consequences for the future agenda for child and adolescent psychotherapy research are discussed.