This study investigates the changes in the Spanish lexical and grammatical skills of 26 Spanish–English dual language learners during their first year of preschool. We also explore the impact of age, gender, and maternal cultural orientation on children’s language outcomes over time. The results show that, despite one year of English-only instruction, the children’s Spanish productions became more intelligible, lexically diverse, and grammatical between 3;7 and 4;7. However, Spanish productions were mostly limited to sentence fragments and contained errors in grammatical gender, verb morphology, object clitic pronouns, and prepositions. Girls had an advantage over boys, as attested by the higher lexical diversity, mean length of utterance, and grammaticality of their Spanish productions. Both maternal enculturation and acculturation predicted the grammaticality of children’s utterances, suggesting that mothers with high levels of orientation to both Latinx and American culture may be the most successful at promoting Spanish in the United States.
