In this chapter we review at some length the present state of the art in the study of the linguistic development in native bilingual speakers (Section 3.1); we further draw attention to linguistic development in consecutive bilinguality (Section 3.2); Section 3.3 describes the specificities of the sign/aural bilingual; in Section 3.4 we discuss how the evidence on bilingual development argues in favour of or against the sensitive-age hypothesis. We finally describe the different cases of attrition in bilinguality (Section 3.5). In the conclusion we discuss how bilingual development can be explained by a more general model of bilingual processing. We do not intend to give detailed linguistic descriptions of the bilingual child's production but rather to give a comprehensive overview of the psycholinguistic factors which can explain bilingual development.

Since the beginning of the twentieth century scholars from a variety of disciplinary backgrounds, such as psychologists, linguists, neurologists and educators, have paid attention to the development of bilinguality; and at the end of the century there has been a research explosion on the subject. During the first half of the century two types of studies were prominent: (1) carefully documented child biographies, such as those by Ronjat (1913) and Leopold (1939–49), and (2) comparative psychometric studies of school tests obtained from bilingual and monolingual children. Whereas the first biographies pointed to a harmonious development of the bilingual child, the early psychometric studies indicated a developmental delay in bilingual children as compared with monolingual peers. This apparent contradiction and the so-called negative consequences of bilinguality are discussed in Chapter 4.