The postsecondary outcomes of individuals with autism spectrum disorder (ASD) are significantly worse than peers with other disabilities. One problem is the lack of empirically-supported transition planning interventions to guide services and help produce better outcomes. We applied an implementation science approach to adapt and modify an evidence-based consultation intervention originally tested with young children called the Collaborative Model for Promoting Competence and Success (COMPASS; Ruble et al., The collaborative model for promoting competence and success for students with ASD. Springer, New York, 2012a) and evaluate it for efficacy in a randomized controlled trial for transition-age youth. Results replicated findings with younger students with ASD that IEP outcomes were higher for COMPASS compared to the placebo control group (d = 2.1). Consultant fidelity was high and teacher adherence improved over time, replicating the importance of ongoing teacher coaching.