Early intervention for toddlers with ASD is critical, given the potential for altering brain development and the increasing focus on early screening and diagnosis. Although several interventions exist, many approaches are time- and resource-intensive, limiting the feasibility of their use in community settings. Parent-implemented approaches are a promising way to achieve the necessary intensity without requiring intensive community resources. However, evidence for the long-term effectiveness of any treatment for toddlers is limited. In addition, not all children have benefited similarly from any treatment, indicating the need to focus on using child characteristics to predict who may be likeliest to benefit from a given intervention. This study will address these needs through a follow-up assessment at ages 5-7 of the 82 participants of an RCT of the Early Social Interaction (ESI) Project, a parent-implemented intervention from 18-36 months. The first aim of this study is to examine long-term outcomes, including commonly used outcome measures (i.e., ADOS, ADI-R, IQ) as well as measures of broader outcomes that affect child and family quality of life (i.e., academic functioning, language, and emotional/behavioral problems and comorbidities). Change from end of treatment to school-age outcome will be examined, as well as maintenance of the effect of earlier (i.e., 18 months) versus later (i.e., 27 months) intensive parent-implemented intervention. Given that most studies find that some, but not all, children show improvement during intervention, it is important to separately examine treatment “responders” and “non-responders”. Children will be classified into groups based on their development during intervention, allowing for examination of differences in child characteristics at the start of intervention between these groups. These results will help clinicians predict whether a child will benefit from parent-implemented intervention. Classification of children into treatment response groups will also allow for comparison of long-term outcomes across response groups, in order to determine if and how change during treatment impacts school-age outcomes. Expected results will lend support to the long-term effectiveness of an early intervention program that is feasible in community settings, and clarify which children experience the greatest improvement from the toddler to school-age years based on how they develop during treatment.