Early experience is not enough: Evidence from differences between heritage and host language trajectories.

A fundamental question for developmental psychology is why effects of early experience only sometimes endure. This question is addressed here with data on the relation of early differences in dual language exposure to children's subsequent bilingual development. The participants were 147 children (74 females) from Spanish-speaking immigrant families in the United States who were studied from the age of 3.5-12 years. Longitudinal mediation analyses linked characteristics of the families (parents' ages of immigration, mothers' education, and the presence of older siblings at home) to early differences in the relative quantity of the children's home exposure to Spanish and English, which, in turn, predicted the children's subsequent rate of expressive vocabulary growth in each language. However, these effects of early experience worked in opposite directions for Spanish and English. Low levels of early home exposure to Spanish were associated with continued slow growth in Spanish vocabulary. In contrast, low levels of early home exposure to English were associated with faster subsequent growth in English vocabulary. These differing trajectories can be explained in terms of the continued reliance of Spanish growth on home exposure and the increasing support for English growth from exposure outside the home. These findings provide examples of predictive relations between early experience and subsequent development that are inconsistent with a process in which early experience creates foundational skills with enduring benefits. The findings suggest instead a process in which observed relations between early experience and later skill result from continuity or discontinuity in subsequent environmental support. (PsycInfo Database Record (c) 2026 APA, all rights reserved).