In countries with public health insurance, caregivers may face long wait times to access services for children with intellectual and developmental disability. This limited access may compromise the adaptation of the child and their family, especially when specialized services (e.g., early intensive behavioral interventions) are needed to manage problem behaviors. Further, longer wait times can contribute to parental stress and increase problem behaviors in children. Therefore, the purpose of the current study was to evaluate the effectiveness of an online parent training for managing problem behaviors for families awaiting specialized services. Twenty-nine families of children with intellectual and developmental disability participated in a randomized controlled trial with random assignment to a waitlist control (i.e., sixteen families in the experimental group and thirteen in the waitlist group). Our results demonstrated that the online training led to reductions in the frequency of problem behaviors and parenting stress while improving caregivers’ self-efficacy. This study provides preliminary evidence for the utility of an online training to support caregivers of young children with intellectual and developmental disability.