Caregiver adherence to treatment plans is likely maintained by negative reinforcement and can contact extinction when child responding relapses. When caregiver adherence contacts extinction, caregiver nonadherence, such as reinforcing their child’s challenging behavior, relapses, threatening treatment efficacy. Previous laboratory models demonstrating the relapse of caregiver nonadherence only evaluated treatment for behavior maintained by social-positive reinforcement, not that maintained by social-negative reinforcement. These models only measured caregiver nonadherence as discrete events, which cannot capture the magnitude of each error. The present study was an evaluation of the relapse of caregiver nonadherence during simulated treatments for escape-maintained challenging behavior. First, caregivers placed demands in a home-like setting and a research confederate responded to these demands in a manner mimicking clinical clients. Next, caregivers were taught to implement treatment in a clinical setting and the confederate’s behavior gradually improved. Last, caregivers returned to the home-like setting and confederate challenging behavior relapsed. Nonadherence relapsed for all caregivers, demonstrating the need for additional research on methods for mitigating caregiver relapse during treatment of children’s challenging behavior and the usefulness of the proposed measurement system for future research.