The Early Development Instrument (EDI) is a holistic assessment of child development that was developed independently of any particular educational curriculum. Studies identify it as a powerful predictor of academic achievement in elementary in many English-language school jurisdictions, including the province of Ontario. Ontario’s French-language schools provide a further test of the EDI’s ability to predict school achievement, since they house a student population exposed to a different curriculum and language of instruction. This article pursues three research questions: (a) Does the EDI predict Grade 3 reading, writing, and math scores among Ontario French-language students? (b) Which EDI domains have the strongest effects? (c) Do any such patterns differ from those found among Ontario’s English-language schools? Data come from 2,696 students in Ontario French-language schools who started kindergarten between 2003/04 and 2005/06 and entered Grade 3 between 2006/07 and 2009/10. Multilevel regression models, controlling for individual- and school-level demographics, find that (a) almost all EDI domains were statistically significant predictors of at least one domain of achievement, and most had significant effects in all three; (b) communication and cognitive skills were the strongest predictors, with effect sizes ranging from .22 to .58, followed closely by socioemotional readiness; (c) these results are similar to those found among Ontario English-language students, except that socioemotional readiness has stronger effects and physical readiness has weaker effects among French-language students. We discuss the EDI’s predictive power across different educational curricula, and why developmental domains may differ in their effects. (PsycInfo Database Record (c) 2022 APA, all rights reserved)