Objective Children with autism have sitting and on-task behavior problems in class. In this study, the effect of three alternative classroom-seating devices such as regular classroom chairs, therapy balls, and air cushions were examined on students' classroom behavior. Materials & Methods 15 students with autism participated in this A1-B-A2-C multiple treatments study from Mashhad's Tabasom School, Mashhad, Iran in 2014. Students' behaviors were video recorded in three phases: sitting on their common chairs during phase A, air-sit cushioned in phase B, and ball chairs in phase C. Sitting times and on-task behaviors were quantified by momentary time sampling and compared during different phases for important changes during 8 wk. Additionally, the Gilliam Autism Rating Scale-Second Edition test was used to examine stereotyped movements, social and communication skills of the students in the before and after research. Results Significant increases in in-seat behaviors in 86.7% (thirteen out of 15) of the students and on-task behaviors in 53.3% of the students (eight out of 15) when seated on therapy balls. Air cushions had no significant effects on in-seat/on-task behaviors. The results also showed significant decrease in stereotyped movement and increase in communication and social skills of these students. The teachers also preferred the use of the balls and/ or air-cushioned chairs for their students. Conclusion Therapy ball chairs facilitated in-seat behavior and decreased autism related behavior of the students with Autism Spectrum Disorder in class.