Short-term and long-term predictors of therapeutic change due to parent management training were investigated. Therapeutic change was defined as the change in outcome measures [externalizing problem behavior and parenting self-efficacy (PSE)] from before treatment to afterward. Three different types of predictors were analyzed: child variables (gender, age, and initial externalizing and internalizing behavior), parent variables (age, initial PSE and parental psychopathology) and socioeconomic status and other sociodemographic characteristics of the family (parental school education, employment, family status, language). The parent management training was part of the Prevention Program for Externalizing Problem Behavior, which was evaluated as an effectiveness trial under routine care conditions using a within-subject control group design. Between 78 and 270 families were included in the analysis, which investigated therapeutic change over two time intervals: (1) immediate change from the pre-treatment to the post-treatment assessments, and (2) long-term-change from pre-treatment to 1-year follow-up. Throughout several analyses, the only predictor of therapeutic change that was consistently significant over the two time periods for the externalizing problem behavior of the child was the initial externalizing problem behavior. More impaired children improved more. Similarly, the only predictor of therapeutic change for the two time periods in PSE was the initial level of PSE. Parents with less PSE gained more during the course of the training.