In this paper we report on a longitudinal study of the linguistic development among Turkish-speaking children in Denmark. A series of data were collected from a group of children attending a public school in Køge during the period 1989-1998 and from the same group--now in their 20s--in 2006-2007. The data set has been analyzed from a number of linguistic and educational perspectives (e.g. second language acquisition, code choice in interaction, language attitudes among teachers and students). In this paper we combine the main lines of the different analyses into a discussion of which terms to use when studying linguistic development in an increasingly diverse world. In particular, we focus on the theoretical distinction between deficit and resource-oriented views on minority children's language development, and we discuss the empirical underpinning of the so-called 4th grade slump which places school underachievement solidly within the children's mastery of specific features of academic majority language. In general, we argue that terms such as "bilingualism" or "multilingualism" are insufficient as descriptive tools. Instead we propose the term polylanguaging to account for our informants' language use in post-modern, superdiverse Danish society.