Research has shown that functional analysis results are beneficial for treatment selection because they identify reinforcers for severe behavior that can then be used to reinforce replacement behaviors either differentially or noncontingently. Theoretically then, if a reinforcer is identified in a functional analysis erroneously, a well researched intervention strategy might fail even when implemented with high integrity. Many studies have demonstrated that functional communication training (FCT) is an effective treatment in reducing severe behaviors while simultaneously shaping an alternative communication response. However, few published studies have systematically evaluated the reasons that underlie failure to acquire the alternative response. In the current study, a functional analysis identified attention as the reinforcer for aggression. FCT to replace aggression was attempted using several different training methods. When aggression persisted and the participant failed to acquire the response to access attention, further functional analyses were conducted. Results of follow-up analyses determined that the participant's aggressive behavior was maintained by attention that led to access to a tangible item or preferred activity. When FCT produced attention to a preferred activity, the participant's aggression reduced to near zero levels. Results of the followup analyses and the combined reinforcers in FCT highlight the utility of an alternative model of functional analysis, and a process for determining when follow-up analysis versus modification of intervention strategies is required. (Contains 6 figures.)