Project Summary Severe destructive behavior represents a comorbid condition of developmental disability for which risk increases with intellectual disability severity, communication deficits, and co-occurring autism spectrum disorder.1,2 Destructive behavior, such as self-injurious behavior and aggression, causes harm to the child and others and increases the risk for institutionalization, social isolation, physical restraint, medication overuse, service denial, and abuse.3 Clinicians have used functional analyses to identify the variables that reinforce destructive behavior and to develop effective, function-based treatments.4-7 Functional communication training (FCT) is an empirically supported, function-based treatment that decreases destructive behavior.8,9 Using FCT, the clinician teaches the child to use a functional communication response (FCR) to request the reinforcer maintaining destructive behavior, while placing destructive behavior on extinction.10-12 For example, if functional-analysis results showed that attention reinforced destructive behavior, the clinician would provide attention when the child used the FCR (“Play with me, please”) and would not provide attention for destructive behavior. Two important limitations of FCT are that (a) schedules of reinforcement maintaining the FCR must often be thinned gradually to levels that are practical for caregivers to implement consistently in the home and in the community,13-15 and (b) this necessary process of reinforcement schedule thinning regularly causes destructive behavior to increase following initially effective treatment, a form of treatment relapse called resurgence.16-19 The current project aims to improve these limitations of FCT by (a) hastening the process of reinforcement schedule thinning by removing unnecessary schedule-thinning steps using the results of a progressive interval assessment20-23 and (b) mitigating the resurgence of destructive behavior by providing stimuli that highly compete with the reinforcer maintaining destructive behavior.23-27 We will conduct a randomized controlled trial to evaluate the extent to which these two promising refinements to FCT improve the process of reinforcement schedule thinning, and an exploratory study will examine the interactive effects of these two approaches. This novel project has the potential to substantially improve standards of care guiding the treatment of severe destructive behavior and to improve the long-term outcomes for children and families afflicted by these debilitating behavior disorders.