ABSTRACT Children with developmental delays and disabilities face persistent challenges in accessing recommended clinic- and school-based therapeutic services, which are critical for supporting developmental, educational, and behavioral outcomes. Studies also show parents benefit when their children receive recommended therapies with improvements in mental health, reduced stress, and enhanced quality of life. Thus, a lack of clinic- and school-based therapeutic services during key periods of brain development, including the preschool years, can substantially contribute to preventable morbidity. Disparities in service access are well-documented among children with developmental delays and disabilities, with Black and Latino/a preschool-age children experiencing some of the lowest rates of receipt of recommended care. In response, the scientific community has called for research to advance understanding of the factors contributing to these health disparities. The objectives of this research are to address the following gaps in the literature: 1) to examine how parental knowledge, school resources, insurance coverage, and neighborhood characteristics, including employment rates and transportation availability, influence access to guideline-concordant school and clinic-based therapeutic services for preschool-age children with developmental delays and disabilities (PCw/DD), and how these factors may affect health outcomes; and 2) to identify modifiable protective factors that may buffer these relationships. Our interdisciplinary team will meet the objectives of this study by conducting a mixed-methods longitudinal study enrolling 300 Black and Latino/a PCw/DD and their parents from clinics across Chicago and collecting prospective data at five time points over three years. We will also convene a Multidisciplinary Advisory Board who will meet biannually to consider how our research findings can inform educational and healthcare practice and policy. The proposed research is significant for its potential to advance scientific knowledge of how aspects of a family’s daily life influence access to school- and clinic-based services; how service gaps and delays impact health outcomes; and the role of key protective factors in mitigating these effects. Results will generate actionable data to guide the development of medical, educational, and public health interventions aimed at improving access to recommended services, supporting family well-being, and promoting optimal developmental outcomes for all children.