One of the focuses of language revitalisation policies is to incorporate minority languages into education. Assessment of new language-of-instruction models is ordinarily based on the growth of minority language speakers. However, it is also essential from an educational viewpoint to explore the potential link between performance and significant variables like economic and cultural status (ESCS) or language background. In the context of the Basque Autonomous Community, where three distinct language-of-instruction models coexist, this paper assays data from a diagnostic evaluation of mathematics skills administered to 16,993 fourth-grade students. Employing multilevel models, the results display an association between linguistic groups and ESCS, and that the link is not strong enough to account for performance differences among groups. The inquiry shows the importance of reckoning with linguistic and socioeconomic background when comparing academic success among language-of-instruction models.