Children with autism spectrum disorder (ASD) are shaped and in turn shape the people in their environment especially those closest to them, their parents and their siblings. When the sibling relationships between children with ASD and their typically developing siblings are considered, challenges and opportunities present themselves for both siblings. This study assessed the effectiveness of a sibling intervention that aimed to meet the needs of both siblings involved. It was initially hypothesised that teaching the typically developing children responsive strategy use would enhance their interactions between the children leading to increases in the quality of the sibling relationship and in the well-being of both siblings. In addition, the typically developing children were given developmentally appropriate information on their sibling’s difficulties, information on emotions, and the opportunity to play mutually enjoyable games with their sibling with ASD to enhance their motivation to persist in attempts at interacting with their sibling with ASD. Initial findings suggested that the planned intervention was not necessarily benefitting the typically developing children. The focus of the intervention changed to include a more explicit focus on the influence of the intervention on the typically developing children. Changes were made, by de-emphasising the strategy component and emphasising the other components, to enable both siblings to benefit from the intervention. Findings indicated that the typically developing children had existing skills for interacting with their siblings with ASD. Increases in the quality of the sibling interactions and the well-being of both children seemed to be most strongly related to aspects of the intervention that increased the warmth of the children’s feelings towards each other and the typically developing children’s understanding and tolerance of their sibling with ASD. Overall, the findings from this project emphasised the importance of supporting family members of children with ASD for the benefit of both the family members and the benefit of the children with ASD.