Chapter 4 explores potential advantages of multilingual upbringing in relation to further language development. It argues that any such advantages play out more forcefully and are easier to identify in regard to general proficiencies rather than specific grammatical phenomena. Chapter 4 further argues that type of bilingualism, as operationalized in terms of language dominance, and the type of language knowledge investigated play a pivotal role for understanding language learning processes against a multilingual substrate. Cross-linguistic influence, as observable in different grammatical domains and the lexicon, can aid additional language acquisition by means of cumulative enhancement, but certain constellations also produce inhibitory effects. The assumption of universally facilitating effects has turned out to be overly optimistic and needs to be tempered. Much of the discussion in Chapter 4 is based on the acquisition of English as an additional language in bilingual heritage contexts (third language acquisition). Besides general CEFR-proficiencies, the case studies concern determiners, subject–verb agreement, tense and aspect, word order, and lexical cross-linguistic influence.

This chapter traces the evolution of language learner autonomy under the impact of transformative classroom practice. It begins by summarizing Holec's definition of the concept, and then describes an approach to teaching and learning that sought to operationalize that definition, but with two added features: use of the target language for all classroom communication; and a strong emphasis on collaborative learning. This gave the concept of language learner autonomy explanatory power: learners acquire L2 proficiency when their agency is channeled through the target language. The chapter then turns to inclusive education, describing an approach to the integration of immigrant pupils that engages their agency by encouraging them to use their home languages in the classroom. This enables them to develop a capacity for agentive behavior in English and Irish with the cognitive support their home language provides. The chapter concludes by briefly associating the two learning environments described with the concept of plurilingualism as it is defined in the Common European Framework of Reference for Languages.