Bilingual children experience more variation in their language environment than monolingual children and this impacts their rate of language development with respect to monolinguals. How long it takes for bilingual children learning English as a second language (L2) to display similar abilities to monolingual age-peers has been estimated to be 4-6 years, but conflicting findings suggest that even 6 years in school is not enough. Most studies on long-term L2 development have focused on just one linguistic sub-domain, vocabulary, and have not included multiple individual difference factors. For the present study, Chinese first language-English L2 children were given standardized measures of vocabulary, grammar and global comprehension every year from 4 ½ to 6 ½ years of English in school (ages 8½ to 10½); language environment factors were obtained through an extensive parent questionnaire. Children converged on monolingual norms differentially according to the test, with the majority of children reaching monolingual levels of performance on the majority of tests by 5 ½ years of English exposure. Individual differences in outcomes were predicted by length of English exposure, mother's education, mother's English fluency, child's use of English in the home, richness/quality of the English input outside school and age of arrival in Canada. In sum, the timeframe for bilinguals to catch up to monolinguals depends on linguistic sub-domain, task difficulty and on individual children's language environment, making 4-6 years an approximate estimate only. This study also shows that language environment factors shape not only early-stage but also late-stage bilingual development.

This study investigated the referring expressions used for first mentions of participants and entities in narratives by Mandarin heritage language (HL) and monolingual children. Referring expressions for first mentions in Mandarin comprise lexical, morphological and syntactic devices. Results showed that HL children used less adequate referring expressions for first mentions than the monolinguals, mainly due to overgeneralization of classifiers and lack of vocabulary knowledge. However, HL children did not differ from monolinguals in their use of relative clauses and post-verbal NP placement to mark first mentions. These results suggest that incomplete acquisition of the HL may vary across different linguistic subdomains (Montrul, 2008); specifically, domains requiring a great deal of input to acquire, such as vocabulary and the large repertoire of classifier morphemes, might be more vulnerable in HL speakers than syntax. Mixed modeling analyses revealed that older age of arrival, higher maternal education levels and a rich and diverse Mandarin environment at home predicted stronger narrative outcomes, also pointing to an important role for input in HL acquisition.

This study examined the phenomena of incomplete acquisition, attrition, and protracted acquisition of the L1 in HL children by focusing on the comprehension and production of subject and object relative clauses (RCs) in Mandarin HL children. A cross-sectional design (study 1) and a longitudinal design (study 2) were both included. Our results showed that HL children were comparable to monolinguals for the comprehension of RCs in both study 1 and 2. For the production of RCs, although monolinguals outperformed HL children in study 1, HL children’s production of RCs was convergent with monolingual-like levels over time (study 2). We conclude that the reduced L1 input HL children receive in the host country does not necessarily lead to deficient acquisition of the L1. Perhaps for some complex structures in the L1 (e.g., RCs), HL children may need more time than monolingual children to accumulate the critical mass of input needed to acquire them.

The cumulative effects hypothesis (CEH) claims that bilingual development would be a challenge for children with specific language impairment (SLI). To date, research on second language (L2) children with SLI has been limited mainly to their early years of L2 exposure; however, examining the long-term outcomes of L2 children with SLI is essential for testing the CEH. Accordingly, the present study examined production and grammaticality judgments of English tense morphology from matched groups of L2 children with SLI and L2 children with typical development (TD) for 3 years, from ages 8 to 10 with 4-6 years of exposure to English. This study found that the longitudinal acquisition profile of the L2 children with SLI and TD was similar to the acquisition profile reported for monolinguals with SLI and TD. Furthermore, L2-SLI children's accuracy with tense morphology was similar to that of their monolingual age peers with SLI at the end of the study, and exceeded that of younger monolingual peers with SLI whose age matched the L2 children's length of exposure to English. These findings are not consistent with the CEH, but instead show that morphological acquisition parallel to monolinguals with SLI is possible for L2 children with SLI.

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