The purpose of this study was to investigate the effects of a function-based intervention on disruptive behavior, active task engagement, and task completion in middle school students with autism spectrum disorder (ASD), and evaluate the maintenance and generalization of the intervention effects. The study was conducted during Korean language classes at a special education middle school and included three students with ASD who had difficulties with active task engagement due to frequent disruptive behavior. Functional behavioral assessments including indirect assessment, direct observation, and functional analysis were conducted to identify the function of disruptive behavior. Based on the assessment results, the function-based intervention was implemented and its effects were evaluated using a multiple baseline across participants design. The experiment consisted of baseline, intervention, maintenance, and generalization conditions. The results demonstrated that the function-based intervention was effective in reducing disruptive behavior and improving both active task engagement and task completion for all participants. These effects were maintained after the withdrawal of the intervention and generalized to a setting in which the intervention was not provided. In addition, the results of the social validity assessment conducted with parents and teachers indicated high levels of satisfaction and acceptance regarding the goals, procedures, and outcomes of the intervention.