In countries throughout the world, educational achievement of young bilingual immigrant children consistently falls behind. Aiming to increase understanding of the processes underlying these language disadvantages, the present 4-wave longitudinal study investigated the relationship between the home language environment and emergent academic language in mono- and bilingual 3- to 6-year-olds. In addition, the study focussed on cross-language associations between bilingual children’s first (L1) and second (L2) language skills. Studying immigrant children in this age range enabled examination of the transition from a home environment in which the first language is predominantly spoken to a school environment in which the second language, the language of the majority, is the standard. A total of 58 monolingual native Dutch, 47 bilingual Moroccan-Dutch, and 56 bilingual Turkish-Dutch children took part in the study. The Moroccan-Dutch children were all of Berber descent and spoke Tarifit as their L1; the Turkish-Dutch children spoke Turkish as their L1. Primary caregivers reported on their language and literacy activities as well as the languages used during these activities via a personal interview. Child assessments included a non-verbal intelligence test, a verbal short-term memory span task, and language tasks addressing a range of language skills that are considered important for school achievement: L1 and L2 standard vocabulary tests, narrative comprehension and production tasks, and a L2 morphosyntactic task. The results showed that despite equal domain general abilities for learning, Turkish-Dutch and Moroccan-Dutch 3- to 6-year-olds persistently scored below the Dutch monolinguals on L1 and Dutch language assessments. The main outcomes of this thesis reveal that these language arrears stem from limited early experiences with language specific literacy and oral language activities: language-specific input in the home environment explained variation in both L1 and L2 proficiency. In addition, findings indicated ...