Introduction

In this chapter, we home in on the interaction of age with the role of participants' knowledge of their background languages – a topic that has been sorely neglected in the literature despite large bodies of research on language transfer and on the age factor in language learning and multilingualism. The following areas of interest lie at the heart of this chapter: the shortand long-term effects of an early start on crosslinguistic influence; the roles of the first language (L1) and the second language (L2(s)) in third language (L3) acquisition, as well as the role of target language (TL) proficiency in the acquisition of lexico-semantics and morphosyntax. In order to explore the causes of, and constraints on, transfer (referring here mainly to negative transfer), particular emphasis will be placed on the discovery of transfer effects in areas of language knowledge and acquisition where transfer has previously been claimed not to occur, or to be relatively rare, such as transfer involving overt inflectional morphology. Furthermore, as there are many circumstances beyond age of onset (AO) and TL proficiency that have an impact on the learning process in general and crosslinguistic influence in particular, we will also take a closer look at perceived and assumed proximity between source and TLs, metalinguistic awareness, motivation, attitudes and self-perception, as well as the influence of the learning environment (e.g. class size and the influence of teaching practices). We are particularly interested in the following questions:

• (1) To what extent do literacy skills in Standard German have an effect on the written development of English as a foreign language (EFL)?

• (2) Are the early classroom learners (ECLs) less affected by crosslinguistic influence (i.e. transfer from Swiss(German) and the intervention of French as an additional foreign language [FL]) than the late classroom learners (LCLs) at the beginning and at the end of secondary school?

• (3) Does the transfer from an additional FL differ from L1 transfer quantitatively and/or qualitatively in the two AO groups?