We propose to analyze the long-term maintenance (up to 2 years) of both reductions in destructive behavior and increases in adaptive behavior achieved via functional communication training (FCT) as a continuation of our currently funded project (HD29402-11 ). To date, we have shown that a treatment package of functional analysis and FCT is often successfully used by parents to reduce destructive behavior and to increase adaptive behavior in young children who have both developmental disabilities and behavioral disorders. In this proposed project, we will specifically study why these positive results occurred by analyzing the operant mechanisms that control adaptive and destructive responding at different points in time. We propose to study the effects of reinforcement and extinction on distinct topographies of both adaptive and destructive behavior over a 2-year period and to evaluate whether changes or interactions occur in these mechanisms over the long-term course of treatment. A four-phase analysis will be conducted to specifically analyze the role of these two mechanisms prior to treatment (Phase 1), during initial treatment (Phase 2), at posttreatment (Phase 3), and during long-term maintenance (Phase 4). Our objectives are to determine (a) the degree of overlap of functional reinforcers across response classes of destructive and adaptive behavior (Objective 1), (b) if changes in functional reinforcers occur within and across topographies over time (Objective 2), and (c) the response strength or persistence of both adaptive and destructive behavior over time (Objective 3) when faced with distinct environmental challenges: changes in establishing operations, discriminative stimuli, or competing reinforcers. These results will increase our understanding of why FCT is often an effective long-term treatment and may identify the conditions under which maintenance is disrupted in natural settings such as homes.