Current research provides evidence of the positive influence of sense of (self-)efficacy and personal experience regarding attitudes towards inclusion for children with special educational needs (SEN). A multilevel study was designed to investigate the relationship between "attitudes towards inclusion" and sense of "efficacy" as well as "mainstreaming experience" at the individual, teaching staff, and principal level. In this context, 48 primary schools with inclusive classrooms were examined. Results indicated that teaching staff differ in regard to "attitudes towards inclusion" and "individual" and "collective efficacy." Furthermore, there was a relationship regarding "attitudes towards inclusion" and "mainstreaming experience" between the school principal and the teaching staff. In regard to factors influencing "attitudes towards inclusion," at the individual level, sense of "self-efficacy" and "mainstreaming experience," and at the teaching staff level, "collective efficacy," influenced "attitudes towards remedial education." Teacher "self-efficacy" significantly influenced "attitudes towards social integration." Results suggest that successful supervision of the process in inclusive school development depends on a consideration of the school's overall framework of circumstances--its principal, its teachers, and its staff.