Who, What, and How? A Scoping Review of Early Intervention Research

Our review explored the following questions: Who is researched, what is researched, and how is research conducted in Part C Early Intervention (EI) in the United States? Guided by Kilbourne's health disparities framework and Bronfenbrenner's ecological systems model, we addressed these questions through a scoping review of 258 peer-reviewed empirical EI studies published between 1988 and 2024. The scoping review process followed and adapted PRISMA guidelines and used team coding with an 86-item data extraction form. It includes data from more than 4.8 million participants, including children, caregivers, and EI-related providers. Our findings indicate that EI scholarship often centers White, English-speaking, urban participants, while racially and ethnically minoritized children and families, multilingual households, rural communities, and U.S. territories are underrepresented or inconsistently reported. Reporting on language, socioeconomic status, nativity, and provider demographics was limited. Furthermore, EI research disproportionately focused on service provision within the EI pipeline, with less attention to referral, eligibility determination, Individualized Family Service Plan development, and transition, and emphasized individual-level child and family factors over organizational, community, and historical factors. Most studies employed quantitative designs, signaling the continued privileging of particular methodological approaches and data sources in EI knowledge production. Understanding who, what, and how EI research is studied is critical, as researchers, journals, and funders function as epistemological gatekeepers whose decisions shape cumulative knowledge, policy, and practice. Our review documents how incomplete demographic reporting, narrow sampling practices, and methodologically constrained approaches contribute to a fragmented and inequitable evidence base. We call for coordinated action across the research-to-practice and research-to-policy pipelines to advance more transparent, contextually grounded EI research that supports equitable access and outcomes in Part C for all children and families.