This article explores language integration from an intergroup-relations’ viewpoint, employing the social identity approach and socio-contextual model of second language acquisition. It centers on the evolution of language attitudes in adolescents as an indicator of cultural integration between the two major language groups in Catalonia. The distinctive features of the Catalan case − the similar ethnolinguistic vitality enjoyed by the two official languages and the widespread bilingualism that common schooling has promoted − make it of great sociolinguistic interest. The empirical inquiry centers on the development of language attitudes towards Catalan and Spanish by using a panel sample of Catalan students (N = 1050) followed for a period of five years (three waves). Joint trajectory clustering was employed to make a longitudinal analysis that displays the main patterns of coevolution. Logistic regression links changes to other linguistic, identity and sociodemographic variables. Results display that there are three major types of change in attitudes: a majority one, whith a profile of integration, and two others, which tend to separation. The direct effects of language confidence and ethnonational identity are found to clarify the likelihood of individuals following one of these types of change.