Literacy is a crucial competence to participate in education and in society. This is also the case for persons with intellectual disability (ID). Indeed, literacy skills enhance their social participation and quality of life. For children with ID and complex communication needs (CCN) - who cannot communicate orally in an intelligible or functionnal manner - literacy skills acquire further significance since they might enable an expansion of their communicational, educational, professional and social opportunities in life. Unfortunately, studies indicate that the majority of persons with ID and CCN enter adulthood without functional literacy skills. Inappropriate teaching practices and the lack of intervention programs adapted to this group of students may explain this phenomenon. Indeed, teaching reading skills to students with ID and CCN is extremely challenging, as these students cannot answer orally (e.g. cannot pronounce the sound corresponding to a letter, cannot read a word aloud). A few studies conducted in English-speaking countries suggest that students with ID and CCN can progress in their reading skills if they benefit from phonics-based and systematic reading instruction programs. However, intervention studies for this group of students with high methodological quality are still extremely scarce. More studies are urgently required to better understand these students’ needs and how to teach them literacy skills efficiently. This research project encompasses three different studies, which took place one after the other: (1) a descriptive study aiming at identifying different profiles in literacy skills among students with ID and CCN using augmentative and alternative communication systems (AAC), (2) a single-case experimental study with multiple baseline across participants aiming at assessing the effects of a phonics-based reading intervention program created for students with ID (de Chambrier, Sermier Dessemontet, & Martinet, 2021) adapted for students with CCN by the research team and integrating revisions on an iPad application (3) a single-case experimental study with multiple baseline across participants aiming at assessing the effects of early literacy lessons adapted by the research team for students with ID and CCN and integrating revisions on an iPad application.