ObjectiveTo examine the relationship between developmental health and neighbourhood socioeconomic status (SES) in kindergarten children with disabilities.DesignCross-sectional study using population-level database of children’s developmental health at school entry (2002–2014).Setting12 of 13 Canadian provinces/territories.MeasuresTaxfiler and Census data between 2005 and 2006, respectively, were aggregated according to custom-created neighbourhood boundaries and used to create an index of neighbourhood-level SES. Developmental health outcomes were measured for 29 520 children with disabilities using the Early Development Instrument (EDI), a teacher-completed measure of developmental health across five domains.AnalysisHierarchical generalised linear models were used to test the association between neighbourhood-level SES and developmental health.ResultsAll EDI domains were positively correlated with the neighbourhood-level SES index. The strongest association was observed for the language and cognitive development domain (β (SE): 0.29 (0.02)) and the weakest association was observed for the emotional maturity domain (β (SE): 0.12 (0.01)).ConclusionsThe magnitude of differences observed in EDI scores across neighbourhoods at the 5th and 95th percentiles are similar to the effects of more established predictors of development, such as sex. The association of SES with developmental outcomes in this population may present a potential opportunity for policy interventions to improve immediate and long-term outcomes.