The goal of this study was to examine key factors that may predict success in school-based mental health interventions. This study occurred in the context of a larger study in which a behavioral, school-based mental health intervention was implemented and evaluated. The children who participated in the intervention (n=30) had been identified as demonstrating significant inattentive and disruptive behavior problems. Treatment outcome was defined as the change in the severity of the child’s behavior across three points in time (baseline, 1-month assessment, post-treatment) as rated by parents and teachers. Predictor variables that were examined included child variables (the child’s intelligence and pre-intervention behavior), family variables (parents’ discipline style, stress associated with their child’s behavior, and involvement in their child’s intervention), and a school variable (the teacher’s degree of optimism regarding the child’s intervention). Data collected were analyzed using mixed model linear regression. A common theme emerged from the analyses—pre-treatment severity of Oppositional Defiant Disorder (ODD) symptoms predicted treatment outcome relatively consistently, i.e., regardless of the rater or the symptom dimension that was used to define outcome. Therefore, the children in our sample who displayed severe symptoms of ODD prior to treatment tended to benefit less from treatment than those who had less severe initial symptoms of ODD. In addition to pre-treatment ODD symptom severity, other variables emerged as significant predictors of outcome (e.g., parenting stress). It is hoped that the knowledge derived from this study can be used to improve school-based intervention programs by better matching them to the characteristics of the children and families that they serve.