Parents and professionals caring for people with autism sometimes encounter baffling, challenging behavior'noncompliance, aggression, or repetitive actions'which they don't know how to stop. The key to resolving problem behavior is to first determine its purpose by conducting a functional behavior assessment (FBA). In this second edition updated with new research, case studies, and anecdotes, the authors explain how clinicians conduct FBAs: measuring behavior; observing behavior and collecting data; and testing the hypothesis about the behavior's function. And now, there's new material about how to do FBAs outside of clinical settings'at school, in the community, and at home'making this strategy more accessible to parents and teachers in daily life. Use the follow-on book, Stop That Seemingly Senseless Behavior! to create effective intervention plans incorporating insights learned from the FBA.