One of the more robust findings in the literature on child language acquisition is that there are large individual differences. Some children pick up language rapidly and with apparent ease. One such case was Roger Brown's ( 1973a) subject, Eve, whose utterances averaged four morphemes at two years and two months. Other children make much slower progress. It took Brown's Adam and Sarah until three and a half years to average four morphemes per utterance.
Similarly, children differ in the rate and ease with which they learn second languages. Some observers believe that it takes about a year for young children learning a second language in a naturalistic situation to reach the level of their peers ( Francescato, 1969), whereas other observers believe that even with very young children a year is not sufficient time to catch up with native-speaking peers ( Valette, 1964). Of course, different observers may use different criteria for comparing second-language learners with native speakers, but careful comparison of children learning a second language naturalistically in similar circumstances clearly reveals a broad range of individual differences in rate and ease of second-language learning ( Ervin- Tripp, 1974; Snow & Hoefnagel-Höhle, 1979; Wong Fillmore, 1976).
The interest in individual differences in first- and second-language development reflects a trend away from emphasis on universal and rule- governed aspects of language learning. This is part of a more general tendency on the part of researchers to devote more attention to the linguistic environment of the child (see Chapter 2) and to patterns of interaction that affect language learning. In this chapter I examine some of the research