Autism spectrum disorder (ASD) is a complex neurodevelopmental disorder whose incidence is rising. School-based professionals are in an ideal position to provide the much-needed assessment and intervention supports for students with ASD, as the professionals' placement within a formal system affords the opportunity to observe and support children in a structured environment. This article will provide school-based psychologists with current information on the clinical features of ASD, best practice assessment and diagnostic approaches for the disorder, and information pertaining to intervention via the use of a clinical case study to inform readers about the clinical reasoning that ensues throughout the process of assessment to intervention.