Immersion in dual-language programs does not impede children's native language processing.

Aims And Objectives: The benefits of dual-language immersion (DLI) versus English-only classrooms for minority-language speakers' acquisition of English have been well documented. However, less is known about the effect(s) of DLI on majority-language speakers' native English skills. Prior studies largely used accuracy-focused measures to index children's language skills; it is possible that processing-based tasks are more sensitive to the effects of DLI experience.

Methodology: Thirty-three monolingual native English-speaking children attending English-only classrooms and thirty-three English-speaking children attending English-Spanish DLI matched in age, gender, nonverbal IQ, and socio-economic status were tested twice, 1 year apart, on standardized and processing-based measures of English vocabulary and morphosyntax.

Analysis: We ran linear mixed-effects models to examine the extent to which group and time would predict scores on knowledge-based measures of vocabulary and morphosyntactic knowledge, as well as accuracy and reaction times on processing-based measures of English vocabulary and morphosyntax.

Findings: Results revealed comparable levels of growth in English for both groups. A subtle effect of DLI was observed on a lexical-decision task: bilinguals were slower in Year 1 but both groups were equally efficient in Year 2. These results indicate that DLI programs have minimal impact on majority-language speakers' native-language skills in the age-range tested.

Originality: This study is the first to longitudinally examine processing-based native language outcomes in bilingual children in DLI classrooms.

Significance: We do not find evidence that DLI exposure carries a cost to native language development, even when indexed by processing measures. This should reassure parents, educators, and policymakers in that there are no downsides to DLI.