In the early 1990s, our group at the University of South Florida initiated a series of studies designed to develop, evaluate, and demonstrate a function-based approach to school-based interventions for the problem behaviors of elementary students with severe emotional and behavioral disorders. Our first step into this research topic was an intensive case study with a 12-year-old girl, "Jill," who had multiple disability labels, including severe emotional disturbance, and whose behavioral challenges had proven resistant to the best efforts of leading experts in numerous fields including neurology, behavioral psychology, psychiatry, applied behavior analysis, and school psychology. The strategy we adopted was just beginning to gain acceptance among behavior analysts working in the area of severe developmental disabilities, as well as the emerging approach known as positive behavior support (Horner et al., 1990), but it had not yet earned recognition in the field of emotional and behavioral disorders. The strategy entailed a process of five steps: (a) descriptive data collection including interviews and direct observations intended to reveal environmental variables associated with especially high and low rates of a target behavior; (b) formulation of hypothesis statements to describe the observed relations between these variables and the designated behavior; (c) direct testing of the hypotheses using experimental methods (ABAB designs) to confirm, reject, and, perhaps, refine the hypotheses (a procedure known as functional analysis); (d) developing and implementing an intervention plan based on the hypotheses; and (e) evaluating the effects of the intervention through systematic direct observations. The case study of "Jill" followed this sequence. After weeks of data collection, four hypotheses were developed and then tested over a 4-day period. The intervention involved several revisions to Jill's curriculum, and it resulted in an elimination of her serious behavior problems and increases in on-task behavior that maintained over the school year. This study (Dunlap, Kern-Dunlap, Clarke, & Robbins, 1991) was the inspiration for the subsequent years of research we conducted on functional assessment and assessment-based intervention with children described as having serious emotional and behavioral disorders. With the support of research grants from the U.S.