Executive function (EF) is fundamental to successful learning and goal-directed behavior in both adults and children. Bilingual experience has been shown to facilitate EF across the lifespan, likely due to the increased cognitive demand required for managing multiple languages on a daily basis. Building on previous research that primarily compared monolinguals and bilinguals categorically, the present study examined whether variation in non-dominant language usage moderates the developmental trajectory of EF in a sample of 71 heterogeneous Spanish-English bilingual preschoolers. Using a general linear model, we found a significant interaction between the proportions of Spanish use, chronological age and performance on an EF task. Results suggest that daily bilingual usage moderates preschoolers’ development in EF. Bilingualism is a multidimensional experience, and for developing children, daily usage is an important quantifiable indicator of bilingualism when considering EF. Research and educational implications are discussed in light of these findings.