The goal of this article is to discuss the risk factors associated with the difficulties school-age children may experience when learning to read. To begin, we suggest that with mandatory public instruction teachers must deal with the full range of students’ aptitude for learning to read. It is estimated that universal teaching, in a regular classroom, meets the needs of approximately 75% of beginning readers. But what about the others? What are the factors that, for them, may hinder reading acquisition? To address this issue, we first discuss the key skills that govern the development of normal readers. Then, we distinguish between two classes of risk factors: individual risks and environmental risks. Known individual risks are associated with heritability, sensory deficits, general cognitive abilities and oral and written language impairments. Known environmental risks refer mainly to literacy activities or instruction in the home or at school. We discuss the nature and the impact of these risk factors on reading acquisition.