In Australia, an increasing number of students with Autism Spectrum Disorder (ASD) are educated in inclusive classrooms. Research shows that teachers' self-efficacy beliefs impact the implementation of inclusionary practices. Eight pre-service teachers and eight recent teacher graduates were interviewed to gain insights into their experiences and perceptions of the inclusion of students with ASD. Specifically, this study explored the types of preparation: (1) university education, (2) experiences with students with ASD, and (3) support from school administration and its impact on participants' self-efficacy beliefs. Results indicated that participants who had more education, training, and previous experiences of engagements with individuals with ASD showed a higher level of self-efficacy. Participants' self-efficacy was linked to hands-on experience, guidance from mentor teachers, ongoing support from teacher-aides and school administration, frequent liaison with parents and professionals, building rapport with students, and undertaking ASD-specific coursework. Extending Bandura's theoretical self-efficacy framework, this study contributes to collective self-efficacy characterised by supportive administrations, colleagues, parents, health experts (e.g. psychologists) and educational authorities. Implications for policy, teacher education programmes and ongoing professional development for teachers are presented, including recommendations on considering wider avenues to increase teacher efficacy.