Growth of lexical and syntactic complexity, accuracy, and fluency in spoken production of first language and second language children

Complexity, accuracy, and fluency (CAF) research has largely focused on competition among the three constructs and their relationship with proficiency. However, it is largely unknown how CAF develops in the course of language acquisition, particularly in children. Furthermore, each construct has been treated as a unified phenomenon rather than as multidimensional. This study thus aims to examine developmental patterns of CAF in spoken production among 29 child L1-Korean L2-English learners in an EFL setting (age: 5–10) and 41 child L1-English learners (age: 4–7). The study measures each of the three CAF constructs in both lexical and syntactic domains, and uses three proxies for target language experience: age for L1 learners; length of learning the target language for L2 learners; and current use of L2 relative to L1 at home for L2 learners. A series of regression analyses show that child L1 learners' lexical accuracy increases with age; child L2 learners' lexical complexity increases with length of learning; and child L2 learners’ syntactic complexity, lexical accuracy, syntactic accuracy, lexical fluency, and syntactic fluency increase with current L2 use at home. These results suggest how certain aspects of CAF develop for both L1 and L2 children, and highlight that different language experience factors shape the development of distinct CAF aspects for child L2 learners. The study also discusses the pedagogical implications of these results for child L2 learners. • This study focuses on speech production in child L1 and L2 learners. • Complexity, accuracy, and fluency (CAF) in lexical/syntactic domains are measured. • Both L1 and L2 children exhibit development in certain aspects of CAF. • Different language experience factors shape the development of distinct CAF aspects. • Current use of L2 relative to L1 affects most CAF indices measured in the study.