The number of young adults with Autism Spectrum Disorder (ASD) is increasing rapidly as ever-larger cohorts of identified children age through adolescence to adulthood. Yet, virtually nothing is known about the services, interventions, and accommodations that high schools already provide, each year, for adolescents with ASD. Who receives them? How effective are they at influencing outcomes in young adulthood after youth exit high school? The study data come from a diverse, nationally representative sample of over 920 youth with ASD followed over 9 years and covering an age span from 13 to 26. This marks an unprecedented opportunity to answer urgent questions in a timely fashion. The aim of this study is to test the impact of interventions that youth with ASD receive during high school on outcomes once they exit high school. Some of the outcomes to be examined include: employment, postsecondary school attendance, service use, social and community participation, and functional independence. The research team can test the impact of many of the interventions commonly received during high school, including age when transition planning began, degree of youth and parent involvement in transition planning, degree of youth inclusion in general education, educational supports and accommodations provided, vocational services, community-based work experience, collaboration with non-school agencies during transition, case management during transition, and independent living skills instruction. The results will provide evidence that is immediately relevant for policy and practice. Understanding which high school experiences predict better young adult outcomes will inform policy and service design and delivery. In addition to testing hypotheses, this study will generate hypotheses to guide future research. Identifying predictors of outcomes and promising interventions in these observational data will inform future efforts to design and test comprehensive interventions for teens with ASD using experimental methods. Lastly, this pilot study will help lay the foundation for a large national cohort study of adolescents and adults with ASD within the next three years.