There has been a rise in autistic pupils in the mainstream classroom. Teachers have often reported frustration caused by a lack of training on managing autistic pupils’ presentations. The aim of this study was to investigate the effect of an online training programme comprising the main paradigms and resources of the Zones of Regulation™ curriculum on teachers’ sense of self-efficacy when managing autistic pupils’ self-regulation needs in the mainstream primary school classroom. Purposive sampling was used to identify primary 5, 6 and 7 teachers with at least one autistic pupil with self-regulation needs in their current class. An occupational therapist with post-graduate qualifications in autism and sensory processing provided a 2.5-hour online training session on the Zones of Regulation™ curriculum for participants. The Teachers’ Sense of Efficacy Scale (TSES) was completed pre- and post-training and at two-month follow-up. The Usage Rating Profile-Intervention Revised was completed post-training and a survey exploring participants’ experience of implementing the Zones of Regulation™ curriculum with their autistic pupils was completed at two-month follow-up. Findings showed that online training in the use of the Zones of Regulation™ curriculum significantly improved TSES scores for teachers (p < 0.001). The curriculum was also shown to be an acceptable, understandable and feasible intervention for primary school teachers in the mainstream classroom. This study suggests that education authorities should consider providing training opportunities on the Zones of Regulation™ curriculum to support teachers in the mainstream classroom. It also demonstrates the important role occupational therapists, with post-graduate qualifications in autism and sensory processing, have in capacity building within education.