This study investigates the oral and written story productions of 56 10-12-year-old Greek-German and Greek-English bilingual children in order find out to which extent their narrative abilities develop conjointly across their two languages and which factors affect this. Quantitative and qualitative measures of narrative discourse ability are related to a composite score of bilingual language dominance (Bilingual Index Score). Results indicate that the degree to which bilinguals can share abilities across their two languages is highly dependent on the type of ability and the degree of dominance and - to a lesser degree - on crosslinguistic differences and modality of production. As such, this study reveals nontrivial implications for the educational support of bi- and multilingual children.