The Individuals with Disabilities Education Act of 1997 mandates the use of positive behavior support (PBS) and functional assessment under certain conditions within the public school setting. In this article the authors review the historical and philosophical tenets of PBS and functional assessment and discuss how specific clinical expertise possessed by schools social workers can be used in these tertiary supports. Given the significant yet emergent role of functional assessment in educational settings, school social workers might aid in the process by configuring teams, collecting information, conducting analyses, and creating interventions on the basis of their clinical training related to mental health and environmental systems. School social workers, by emphasizing their utility within functional assessment, expand opportunities for evidence-based practice and better student outcomes.