(ASD) now exceeds other severe developmental disorders, making it a significant public health concern [1]. Timely administration of effective treatments is crucial [2] but knowledge of how to tailor treatments to particular children is incomplete. This is evidenced by inconsistent findings, where some children make expressive language gains, while others remain minimally verbal [3]. Further inquiry is necessary to the purpose of better customizing treatments to increase language gains across various populations.Intervention approach is an active ingredient that may contribute to outcome variance, but other factors can alter response to the intervention. Proponents of dynamic systems theory (DST) posit that people have multiple, complex systems outside themselves, such as the home, neighborhood, community, school, workplace, and the people therein, that interact with the inherent developmental processes [4]. This theory exPurpose: Eight language and autism related journals published between 1993 and 2017 were analyzed to identify trends in the inclusion of underrepresented populations in empirical studies with social skill, play, joint attention, and expressive language outcomes. Relationships among treatment outcomes, treatment settings, and underrepresented population types were explored.Methods: All articles (12,381) were searched to identify intervention studies that included participants with autism and were classified by treatment target and setting (N =291). The selected studies were then examined to determine if any participants were from underrepresented populations (n=138) and categorized by type of underrepresented population.Results: Most studies did not indicate demographic characteristics beyond disability, age, and gender; and few relationships between frequency of underrepresented population articles, treatment targets, or intervention setting emerged. Results indicated that demographic characteristics were often omitted, despite recommendations to report descriptive information.Conclusions: Although inclusion of underrepresented populations has increased since 1993, treatment study results cannot yet be generalized to a more diverse population, due to the disproportionately low number of participants from racial/ethnic minority, multilingual, and low socioeconomic status groups reported and/or included in studies. The dearth of underrepresented participants suggests that conscious efforts to recruit and report them are still necessary.