Symptoms of Autism Spectrum Disorder (ASD) including impairments in social communication and the presence of restricted and repetitive behavior (RRBs) are present in the first 2 years of life, prior to diagnosis. This study compared two developmental models describing the early emergence of ASD symptoms, Social Motivation and Attention theories, in a community-based sample of infants who were followed from 12 months of age into early childhood. Participants included 43 children identified at high-risk for a later diagnosis of ASD based on a positive screen on the First Year Inventory (FYI) at 12 months of age. Toddlers were evaluated at 13 and 22 months, followed by a diagnostic evaluation at 3-5 years. Video coding for social motivation (looking at people) and difficulty disengaging attention (shifting of attention and RRBs) was completed at 13 and 22 months. Path analyses were conducted to evaluate the direct and indirect effects of measures of looking at people, attention shifting, and RRBs on ASD symptom severity. Results indicated a significant indirect effect from decreased looking at people at 13 months to decreased attention shifting at 22 months to increased ASD symptom severity at age 3-5 years. Further analyses indicated that this indirect effect remained when only examining social-specific shifting (i.e., attention shifting including a person) but was not present when only including non-social shifting (i.e., shifting attention between objects). Results from this study better support the Social Motivation theory of the early emergence of ASD symptoms than the Attention theory. While impairments in attention clearly play an integral role in later diagnosis of ASD, attention shifting that included social information appears to play a larger role than attention shifting to non-social information. Further, results suggest that RRBs appear to develop separately and in parallel to symptoms of decreased looking at people and attention shifting involving people. Further examination of how these early symptoms predict later school-aged outcomes (e.g., symptom severity, comorbid attention difficulties, etc.) is needed to gain a further view of the developmental processes in ASD.