There is a severe shortage of services for children with autism in Ethiopia; access to services is further impeded by negative beliefs and stigmatising attitudes towards affected children and their families. To increase access to services, care provision is decentralised through task-shifted care by community health extension workers. This study aimed to examine the impact of a brief training (Health Education and Training; HEAT) for Ethiopian rural health extension workers and comprised three groups: (1) health extension workers who completed a basic mental health training module (HEAT group, N = 104); (2) health extension workers who received enhanced training, comprising basic HEAT as well as video-based training on developmental disorders and a mental health pocket guide (HEAT+ group, N = 97); and (3) health extension workers untrained in mental health (N = 108). All participants completed a questionnaire assessing beliefs and social distance towards children with autism. Both the HEAT and HEAT+ group showed fewer negative beliefs and decreased social distance towards children with autism compared to the untrained health extension worker group, with the HEAT+ group outperforming the HEAT group. However, HEAT+ trained health extension workers were less likely to have positive expectations about children with autism than untrained health extension workers. These findings have relevance for task-sharing and scale up of autism services in low-resource settings worldwide.