This study examined the role of the replacement behavior when designing function-based interventions. Three students with Autism Spectrum Disorder (ASD) ages 12, 5, and 6, who displayed chronic off-task behavior participated in the three-phase study. In Phase 1, a descriptive functional behavioral assessment (FBA) was conducted for each student, and then each student's ability to perform the replacement behavior was assessed using a two-step approach. In Phase 2, two function-based interventions were designed for each student using the Decision Model (Umbreit, Ferro, Liaupsin, & Lane 2007). The first intervention consisted of methods to adjust antecedent and consequent contingencies of reinforcement alone, whereas the second intervention included methods to teach the replacement behavior. In Phase 3, the function-based interventions were implemented during typically occurring classroom activities for five weeks. For students who did not already perform the replacement behavior independently, the interventions that included strategies to teach the replacement behaviors produced more favorable results than the interventions that did not. High levels of treatment integrity and social validity were obtained.