Functional assessment procedures have proven useful for developing effective individualized interventions for a wide variety of populations and behavioral concerns. However, fewer studies have been conducted with preschool students who exhibit high incidence problem behaviors. The current study includes data from comprehensive functional assessments and interventions implemented in preschool and Head Start classrooms. Three preschool students and five teachers participated in the study. Each student received a comprehensive functional assessment for problem behavior that included a teacher interview, descriptive assessment, and abbreviated functional analysis. Assessment data were used to develop individualized function-based interventions that were implemented by experimenters and teachers. The function-based interventions resulted in decreases in problem behavior for all three students. Additionally, convergence between functional assessment procedures was obtained for all participants. Finally, social validity data indicated that teachers found the assessment and intervention procedures acceptable.