The Effect of Dual Language Exposure on Single Language Development: Comparing Acquisition Rates in Bilingual and Monolingual Children

A central question in bilingual child language acquisition research concerns the effect of dual language exposure on the rate of language development. Previous research has produced conflicting evidence: While some studies have reported similar acquisition rates, other studies have found that bilingual children lag behind their monolingual peers in their vocabulary and grammatical development. The goal of the present study was to contribute to this ongoing debate by investigating acquisition rates in bilingual and monolingual children in single language comparisons. Fifty German kindergarten children aged from 4 to 6 years old participated in the study: 25 German-speaking monolingual children (mean age 63 months [SD=7.5 months]) and 25 bilingually developing children who acquired German in combination with another language (mean age 64 months [SD=8.3 months]). We compared acquisition rates of three global measures (MLU, vocabulary size and vocabulary growth rate) and five local measures of language performance that served as proxies for the assessment of the degree of development of complex sentences with adverbial clauses. We found that – with the exception of MLU – the monolingually developing children were significantly more advanced on all measures of language performance. Implications for understanding bilingual development are discussed.