Population health begins in early childhood: Kindergarten EDI school readiness scores as a predictor of sixth-grade academic outcomes in the USA

School readiness skills in early childhood are strongly linked to later academic performance, health, and overall quality of life. Various tools, including the Early Development Instrument (EDI), have been used to assess children’s school readiness skills. The EDI is an internationally utilized, holistic measure used to monitor population trends in developmental health and school readiness in early childhood. Although EDI scores demonstrated associations with later academic achievement in several countries, only one study in the United States has examined the EDI’s predictive validity for third-grade outcomes. To expand this knowledge, the current study investigated the psychometric properties of the EDI in the United States, focusing on sixth-grade outcomes. Using a sample of kindergarteners (N = 2610) from five school districts in Orange County, California, this study examined whether kindergarten EDI scores predict academic proficiency in mathematics and English language arts by sixth grade. Findings show that kindergarten EDI scores are strong predictors of sixth-grade academic performance. Children classified as vulnerable or at risk in one or more EDI domains showed significantly lower proficiency in both mathematics and English language arts compared to their peers who were on track. Additionally, disparities in academic outcomes were observed across factors such as sex at birth, ethnoracial background, individualized education plan status, and eligibility for free or reduced-price lunch. Implications for early childhood population health are discussed.