This empirical study investigates the acquisition and development of nominal morphology in L1-English-speaking children acquiring German as a second language in an immersion school context. The focus is on accuracy development in the emerging German article system. Embracing theoretical and applied aspects of second language acquisition research, the study brings together educational, cognitive and psycholinguistic dimensions of second language learning and teaching. Results have implications for curriculum design and quality development in language immersion and content and language integrated learning.