We investigate the causal effect of parents’ linguistic skills on the intergenerational language transmission in a bilingual society. We consider the case of Catalonia, where the two main speech communities, Spanish and Catalan, are of similar sizes, and both languages are official, and exploit the natural experiment generated by a language-in-education reform. We discuss theoretically the main alternative channels through which such policies may affect the language parents speak to their children. Empirically, we find that the reform improved oral skills in Catalan among native Spanish speakers. These greater skills increased the propensity to speak Catalan with the offspring, which highlights the intergenerational spill overs of the reform. We also show that the effect is not confounded by spurious trends, potential changes in language identity, and linguistically mixed partnership formation.