Mean Length of Utterance (MLU) has been widely used to measure children’s early language development in a variety of languages. This study investigates the utility of MLU to measure language development in four agglutinative and morphologically complex Southern Bantu languages. Using a variant of MLU, MLU3, based on the three longest sentences children produced, we analysed the utterances of 448 toddlers (16-32 months) collected using the MacArthur-Bates Communicative Development Inventory, a parent-report tool. MLU3, measured in words (MLU3-w) and morphemes (MLU3-m), significantly correlated with age and other indices of language growth (e.g., grammar and vocabulary). MLU3 measures also accounted for significant variance in language development particular morphosyntactic development. Our results suggest that MLU3-m is a more sensitive measure than MLU3-w. We conclude that MLU measured in morphemes provides a useful addition to other indices of language development in these kinds of morphologically complex languages.

Much research has focused on the expression of voluntary motion (Slobin, 2004; Talmy, 2000). The present study contributes to this body of research by comparing how children (three to ten years) and adults narrated short, animated cartoons in English and German (satellite-framed languages) vs. French (verb-framed). The cartoons showed agents displacing themselves in variable Manners along different Paths (Path saliency and variance were specifically manipulated in four item types). Results show an increase with age across languages in how much information participants expressed. However, at all ages, more motion information was encoded in English and German than in French. Furthermore, language-specific features impacted the content and its organization within utterances in discourse, showing more variation within and across Path types in French than in the satellite-framed languages, resulting in later achievement of adult-like descriptions in this language. The discussion highlights the joint impact of cognitive and typological features on language development.

A fundamental goal of linguistic theory is to explain how natural languages are acquired. This paper describes some recent findings on how learners acquire syntactic knowledge for which there is little, if any, decisive evidence from the environment. The first section presents several general observations about language acquisition that linguistic theory has tried to explain and discusses the thesis that certain linguistic properties are innate because they appear universally and in the absence of corresponding experience. A third diagnostic for innateness, early emergence, is the focus of the second section of the paper, in which linguistic theory is tested against recent experimental evidence on children's acquisition of syntax.