This study examines Thai university students' perceptions of Interactive Response Systems (IRSs) in fully online English instruction, addressing the limited research on their use in virtual classrooms. A mixed-method approach, involving surveys and interviews with 289 participants, revealed generally positive perceptions of IRSs as tools that enhance engagement, motivation, and goal achievement. Female students reported higher satisfaction and comprehension, while frequent users experienced stronger engagement and learning outcomes. Students with a preference for English expressed more favorable views of IRSs, particularly in aiding comprehension and achieving learning goals. However, challenges such as technical issues, pacing, and consistent implementation were highlighted, particularly by less frequent users. By focusing on IRSs in fully virtual environments, this study contributes to the under-explored area of IRS applications in online English instruction.