Purpose: The study examined the effect of bilingual input on the grammatical development of bilingual children in comparison to monolingual peers.
Method: Spontaneous language samples were collected in English and French from typically-developing bilingual and monolingual pre-schoolers aged 3 years (n = 56) and 5 years (n = 83). Within each age group, children varied in bilingual exposure patterns but were matched on age, non-verbal cognition, maternal education and language status, speaking two majority languages. Measures included mean length of utterance (MLU) in words and morphemes, and accuracy and diversity of morphological use.
Result: Grammatical development in each language was strongly influenced by amount of same-language experience. Children with equal exposure to both languages scored comparably to monolingual children in both languages, whereas children with unequal exposure evidenced similarly unequal performance across languages and scored significantly lower than monolinguals in their weaker language. Scoring significantly lower than monolinguals in both languages may, therefore, be a sign of language impairment. Each language followed a strongly language-specific sequence of acquisition and error patterns. Five-year-old children with low exposure to English displayed an optional infinitive pattern, a strong clinical marker for Primary Language Impairment in monolingual English-speaking children.
Conclusion: Descriptive normative data are presented that permit more accurate interpretation of bilingual assessment data.
Keywords: Bilingualism; assessment; language impairment.