Three students with autism spectrum disorder (ASD) who displayed off-task behavior participated in a two-phase study. In Phase 1, a functional behavioral assessment (FBA) was conducted for each student. In addition, an assessment of each student's ability to perform the replacement behavior identified that none of the participants was able to do so. In Phase 2, two function-based interventions were designed for each student. Both interventions included identical reinforcement and extinction procedures but different antecedent conditions. One intervention prompted performance of the replacement behavior. The other directly taught the student how to perform the replacement behavior. Both interventions were tested during classroom activities. For these students, the intervention that included teaching the replacement behavior produced high levels of on-task behavior. In contrast, the intervention without direct instruction produced much lower on-task levels that were only marginally higher than baseline. Implications for intervention design are included.