How parents support social learning at the preverbal level for toddlers with autism is rarely reported, limiting the field's understanding of factors that may influence early development of social competency. As a central challenge in autism that is resistant to intervention, preverbal social initiating is an important indicator of social motivation. This study explored parents' application of mediated learning principles. Mediated learning theory is based on active engagement in the learning process or "learning to learn" and the Joint Attention Mediated Learning intervention applied the principles to child and parent learning. The investigation explored associations between parents' application of mediated learning principles with unprompted initiation of joint attention for 119 toddlers with autism. Post-intervention videos of unstructured parent-child interaction were used to analyze parents' application of the principles and child initiation of joint attention. Significant differences were found between intervention and control conditions in parents' mediation of child learning. In a multiple regression analysis of associations between parents' application of the principles and toddler initiation of joint attention, parents' success in applying mediated learning principles predicted toddlers' initiation of joint attention gains. Considered individually, the strongest predictor of initiation of joint attention was the principle Giving Meaning with the principle Encouraging also showing significance.