Individual variation in second-language acquisition

Individual variation in second-language acquisition is the study of why some people learn a second language better than others. Unlike children who acquire a language, adults learning a second language rarely reach the same level of competence as native speakers of that language. Some may stop studying a language before they have fully internalized it, and others may stop improving despite living in a foreign country for many years. It also appears that children are more likely than adults to reach native-like competence in a second language. There have been many studies that have attempted to explain these phenomena.

A flurry of studies in the 1970s, often labelled the "good language learner studies", sought to identify the distinctive factors characteristic of successful learners. Although those studies are now widely regarded as simplistic, they did serve to identify a number of factors affecting language acquisition. More detailed research on many of these specific factors continues today. For this reason, individual variation in second-language acquisition is not generally considered a single area of research. Rather, it is simply a convenient way to categorize studies about language aptitude, age and language learning, strategy use, and affective factors that affect language acquisition.