Recent efforts to improve American educational practices have focused on determining the efficacy of interventions and instructional practices via randomized controlled trials. Aligned with this effort, the Institute for Education Sciences (IES), the primary funding agency for experimental research in education, has organized grant funding into goals which include Development and Innovation (Goal 2) in order to ready interventions for an efficacy trial. The literature, however, provides little guidance for conducting the iterative process of intervention required to develop an intervention. We describe a multi-phase process that we used to develop a comprehensive intervention package for secondary age students with social, emotional, and behavioral problems. The intervention package was developed as part of the Center for Adolescent Research in the Schools (CARS) in preparation for an efficacy trial.