<p>The goal of this study was to develop a comprehensive Theory of Change of caregiver coaching processes for an early social communication intervention for young autistic children, with attention to the caregiver learning process and a full constellation of outcomes for the caregiver and family unit. We interviewed intervention experts (n = 10), community providers (n = 22), and caregivers (n = 12) about their knowledge and experiences with a parent-mediated intervention (Project ImPACT), guided by the Theory of Change Framework. Qualitative interviews were transcribed and coded using the Framework Method and causation coding. We developed a comprehensive causal model which describes how both learning and motivational processes contribute to caregivers’ implementation of the intervention, as well as broader outcomes with regard to sustainment, quality of life, advocacy, and goals and expectations. We also identified aspects of service need and contextual fit which inform the broader context for our theory of change. This study identified two mechanistic processes by which caregiver coaching impacts relevant short- and long-term caregiver and family outcomes, informed by practice-based knowledge. In the future, these findings can be used to guide empirical research that directly tests the mechanistic processes underlying effective parent-mediated interventions for young autistic children.</p>