Purpose: This longitudinal study investigated the trajectory of Spanish article accuracy in Spanish–English dual language learners (DLLs) from preschool to first grade, addressing the need for longitudinal data on the variability of Spanish grammatical skills in DLLs in English immersion classrooms. Method: Language sample analysis was conducted on 336 Spanish and English narrative retells elicited from 31 Spanish–English DLLs (range: 45–85 months). Growth curve models captured within- and between-individual change in article accuracy from the beginning of preschool to the end of first grade. Results: As a group, DLLs did not exhibit significant positive or negative growth in Spanish article accuracy over time. On average, article accuracy remained stable at 76% from preschool throughout first grade. Participants exhibited significant variability in article accuracy that was partly explained by changes in Spanish proficiency. Spanish article accuracy was lower for DLLs with lower Spanish proficiency indexed by measures from the Spanish language samples, while English proficiency indexed by the English language samples did not affect Spanish article accuracy. Conclusions: These findings suggest that expectations for Spanish grammatical performance in DLLs need to be adjusted to account for the possible impact of not receiving Spanish support in English immersion school settings. DLLs in these instructional programs do not exhibit article accuracy at a level expected for monolingual Spanish speakers. Significant individual differences in both individual status and growth rates of Spanish article accuracy highlight the broad variability in Spanish language skills of DLLs in the United States.