Using data from a statewide couple relationship education (CRE) program efficacy study, this implementation science study considered whether and how classmates influence gains from CRE exposure. We pursued a theoretically and empirically supported model to explore whether class climate, indicated by classmate characteristics, influenced change in individual and relational outcomes. CRE research had not explored the potential impact of the classmate characteristics as has been explored in school-based education studies. Previous CRE researchers have given limited attention to the unique shared experiences during CRE, combining data from different classes and sites, and have been unable to parse out the relative variation at the individual, couple, and class levels. Expanding upon a recently published efficacy study that demonstrated program impact across several domains for the average CRE participant, we used multilevel modeling to explore whether classmate group characteristics (i.e., class average income, perceived stress, and couple relationship quality) influenced residual change for each separate gain (i.e., immediate changes in self-care or conflict management skills, and long-term changes in mental health, relationship quality, or family harmony experienced one year later) above and beyond participant baselines. Findings indicated that (a) class economic disadvantage resulted in more short-term skill gains, but had no influence on long-term functioning gains, (b) the influence of class stress on short-term gains depended on personal stress (lower stressed participants had less self-care gains in highly stressed classes, yet higher stressed participants had less conflict management gains in highly stressed classes), and less class stress resulted in more long-term mental health benefits; and (c) higher class relationship quality was associated with more gains for all short-term skills and long-term functioning. Therefore, class average relationship quality appears to be a critical class-level risk or protective factor for individual class benefit. We improved the ability to predict individual variation and identified some classmate characteristics that can be assessed at program start and considered in program design and delivery. Moving beyond evaluation studies centered on the "average" experience, this study serves to expand the growing body of CRE implementation science studies providing implications for developing best practices for diverse populations of CRE participants. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://www.proquest.com/en-US/products/dissertations/individuals.shtml.]