Résumé : Studies examining reading development in bilinguals have led to conflicting conclusions regarding the language in which reading development should take place first. Whereas some studies suggest that reading instruction should take place in the most proficient language first, other studies suggest that reading acquisition should take place in the most consistent orthographic system first. The present study examined two research questions: (1) the relative impact of oral proficiency and orthographic transparency in second-language reading acquisition, and (2) the influence of reading acquisition in one language on the development of reading skills in the other language. To examine these questions, we compared reading development in French-native children attending a Dutch immersion program and learning to read either in Dutch first (most consistent orthography) or in French first (least consistent orthography but native language). Following a longitudinal design, the data were gathered over different sessions spanning from Grade 1 to Grade 3. The children in immersion were presented with a series of experimental and standardized tasks examining their levels of oral proficiency as well as their reading abilities in their first and, subsequently in their second, languages of reading instruction. Their performances were compared to the ones of French and Dutch monolinguals. The results showed that by the end of Grade 2, the children instructed to read in Dutch first read in both languages as well as their monolingual peers. In contrast, the children instructed to read in French first lagged behind the other Dutch-speaking groups in Dutch reading tasks. These findings extend the notion that differences across languages in terms of orthographic transparency impact on reading development to the French-Dutch pair, and strongly support the view that there are potentially significant benefits to learning to read in the most consistent orthographic system first, even thought it is the least proficient language, since it boosts phonological processes and improves subsequent reading acquisition in both languages.