The academic achievement of boys with fragile X syndrome and the relation between several predictive factors and academic performance are reported. Boys with fragile X syndrome displayed significant deficits in all academic skill areas. Relative strengths were observed in general knowledge, reflecting the ability to integrate experiential information. In contrast, relative weaknesses were observed in prewriting skills and visuospatial-processing abilities. The rate of academic growth slowed over time, and the decrease in rate was more pronounced in measures of core academic skills (e.g., prereading and math skills) than in broad-based tasks. Nonverbal IQ and FMR protein expression were not associated with the level or rate of change; however, autistic behavior and maternal education were related to academic achievement scores.