Developmental disabilities (DDs) affect the health of many children nationwide. Access to therapy services (e.g., speech and language therapy, occupational therapy) for children with DDs can help to optimize their health across the lifespan. Policy initiatives such as state Medicaid Home and Community Based Services (HCBS) waivers intended to improve therapy access for school‐aged children with DDs may benefit from increased knowledge of therapy access state variation and determinants. This study aimed to (1) determine whether significant state variation in therapy access exists and (2) examine associations of child, parent or family, neighborhood, healthcare, and state determinants with therapy access among US school‐aged children with DDs.This was a secondary analysis of individual level data from the 2016 and 2017 National Survey of Children’s Health and state level data from the 2016 American Community Survey, 2016 Health Resources and Services Administration, 2015‐16 Office of Special Education Programs, and 2016 Centers for Medicare and Medicaid Services. The dependent variable was if the child was currently accessing therapy services to meet his/her developmental needs. Independent variables examined included characteristics of the child (e.g., age), parent or family (e.g., income), neighborhood (e.g., neighborhood amenities), healthcare (e.g., medical home), and state factors (e.g., number of state HCBS waivers targeting children with DDs). We fit weighted multilevel regression models to examine therapy access variation and determinants across states.The sample included 9,984 US children ages 6‐17 years with ADHD, learning disability, developmental delay, speech and language disorder, ASD, blindness, deafness, intellectual disability, epilepsy, cerebral palsy, Tourette syndrome, and/or down syndrome. The sample represented 19% of the US child population ages 6‐17 years.Overall, 34.6% of school‐aged children with DDs were accessing therapy services. Statistically significant variation in therapy access for children with DDs was found across states (σ2 = .11, SE = .04, Range: Iowa = 21.7%, D.C. = 51.1%). Older child age and private insurance were each associated with significantly lower adjusted odds of therapy access. Functional limitations, individualized education program, frustration accessing services, and care coordination need were each associated with significantly higher adjusted odds of therapy access. Bivariate analysis results showed lower number of medically underserved areas, higher percent of children with IDEA Part B services, and higher number of HCBS waivers per state were each associated with higher odds of therapy access; however, these associations did not remain statistically significant in multivariable analysis results. Multivariable analysis results for children with DDs in waiver states demonstrated higher estimated annual costs per child to be associated with lower adjusted odds of therapy access (aOR = 0.85; 95% CI: 0.81‐0.90). Sensitivity analysis results also showed that among children with DDs and functional limitations, ≥2 state HCBS waivers were associated with increased adjusted odds of therapy access.Therapy access for school‐aged children with DDs varies widely across states, reflecting geographic disparities in care. Results further highlight pronounced disparities in therapy access by age, insurance, and service needs among school‐aged children with DDs.To advance equitable access to therapy services for school‐aged children with DDs, targeted policy and practice initiatives remain needed.Agency for Healthcare Research and Quality.