The PEAK Relational Training System was designed as an assessment instrument and treatment protocol for addressing language and cognitive deficits in children with autism. PEAK contains four comprehensive training modules: Direct Training and Generalization emphasize a contingency-based framework of language development, and Equivalence and Transformation emphasize an approach to language development consistent with Relational Frame Theory. The present paper provides a comprehensive and critical review of peer-reviewed publications based on the entirety PEAK system through April, 2017. We describe both psychometric and outcome research, and indicate both positive features and limitations of this body of work. Finally, we note several research and practice questions that remain to be answered with the PEAK curriculum as well as other many other autism assessment and treatment protocols that are rooted within the framework of applied behavior analysis.