A critical measure of intervention effectiveness is durability over time. Still, few studies have examined the long-term outcomes of support derived from a functional behavioral assessment as well as enablers and barriers that contribute to or impede successful outcomes. In the current study, a functional behavioral assessment was conducted with a 10-year-old boy with developmental disabilities who engaged in high-rate aggression. Based on the assessment results, a comprehensive support plan was developed and implemented, which resulted in a decrease in aggression and increase in activity engagement. His subsequent progress was followed for 3 consecutive school years. This longitudinal follow-up indicated that components of the plan remained effective; however, illness and implementation lapses resulted in decrements in progress. (Contains 2 figures and 2 tables.)