The relationship between a functional assessment-based parent intervention and preschoolers' challenging behaviors was examined in the current study. A single subject design with a multiple baseline across 2 parent-child dyads was implemented. The researchers collaborated with parents to design the FA-based interventions and parents received varying levels of support throughout the study. Results indicate that parents were able to implement the functional assessment-based interventions, and these interventions effectively reduced children's challenging behaviors. In addition, parents continued implementing the intervention strategies following termination of the intervention, and children's challenging behaviors remained low.