In the face of transnational mobility and migration, globally networked communities and super-diverse social environments, traditional research practices of speaker categorization such as the distinction between native and non-native speakers, first, second, and third language users and mono-, bi-, and pluri-/multilinguals, which rest on the assumption of categorical differences between types of speakers and the general stability of speaker categories as biographical fact, are increasingly called into question. Critical voices point out that in real life, differences between language users turn out to be fuzzy, gradient, and continuous, and that conventional speaker categorizations are conceptualized from a monolingual perspective, providing grounds for discriminatory practices. Based on a longitudinal study design, the paper aims to offer an alternative quantitative approach for researchers who are dissatisfied with common practices of speaker categorization and wish to shift perspective to a more comprehensive way of studying language development within communities. The analysis draws on the results of c-tests for German, Italian, and English that were specifically designed for the study and administered to the same students (n = 170) in their first and final year at lower secondary school.