The Early Development Instrument (EDI) is a community-based measure of young children’s developmental health and early learning intended to identify areas, both developmentally and geographically, in which children have the greatest need and require the most supports. It is a population measure that is based on developmental rather than curriculum benchmarks, and it assesses five general areas, or domains, of child development: physical health and well-being, social competence, emotional maturity, language and cognitive development, and communication skills and general knowledge). EDI data are collected through a questionnaire that senior kindergarten teachers complete for all children in their classrooms every three years. Three measures of children’s developmental health are included in the analysis of the York Region EDI results: “scoring low” (or EDI vulnerability), meeting of “few/no” developmental expectations, and domain averages. All measures are assessed separately for each of the five developmental domains. “Scoring low” is the most widely used measure. Data are reported at the regional and neighborhood level.