Many parents and professionals believe that learning to speak, read and write in two languages can lead to academic deficiencies due to cognitive overload and the risk of confusion linked to handling two language codes. Therefore, some bilinguals abandon or are tempted to abandon one of the two languages, often the first language, in exchanges with their children, in favor of the language of schooling. However, all recent scientific data tend to show that bilingualism is an asset more than a handicap. Nevertheless, these positive results most often concern English-speaking contexts and are not directly transposable to a French-speaking context. Drawing on the results of our work carried out in Oceania and in other territories, this article will deal with bilingual development and the impact of educational systems that promote the heritage or local languages from primary school. More specifically, the oral language of the bilingual, biliteracy and the effects of cross-linguistic transfer will be addressed. Results from both longitudinal studies in New Caledonia and French Polynesia, confirmed by other studies conducted in Sub-Saharan African, show a positive effect of the bilingual education curriculum on local language (Drehu and Tahitian) skills without having negative effects on French. We demonstrated that the expected effects of cross-linguistic transfer are only possible if the pupils learn to read and write in the two languages (local language and French). Additionally, learning to read in one of those local languages makes it easier to learn to read in French, which has a more opaque writing system.