The present study aims to investigate whether language programmes influence students’ written appropriateness in the two official languages of the curriculum (Spanish and Catalan). Additionally, it examines the impact of language spoken at home on L3 (English) writing. A total of 392 primary students in the Valencian Community from three state schools with different intensity of exposure to the three languages of the curriculum participated in the study. Data were collected using an elicited written task and a questionnaire. Findings from the study show that hours of language exposure in the classroom do not always explain students’ written appropriateness in Spanish and Catalan, suggesting that out-of-school factors may play a role. Considering language at home, the study confirms previous research pointing out that students who use a minority language at home perform better in both Spanish and Catalan writing. Finally, in relation to L3 (English) writing, our results support previous research in the area of multilingual pragmatics, showing that being bilingual (Spanish and Catalan) has an impact on students’ L3 (English) written appropriateness. The study offers insights for language educators and advocates for a multilingual approach in education, emphasising the need for balanced language programmes that foster linguistic diversity at school and beyond the classroom.