The prevalence of the fragile X mental retardation (FMR) 1 and FMR2 full mutations (fM) was examined among 1014 school-age children with academic difficulties but without mental retardation. Both Southern blot and polymerase chain reaction analyses for FMR1 and FMR2 were performed on samples obtained from these children. No fM genes were found, and one FMR1 premutation was identified. The distribution of allele sizes for both genes was comparable to those reported for other clinical and normal population samples. These results suggest that neither the FMR1 nor the FMR2 mutation is a common etiology of academic failure among school-age children without mental retardation and that the prevalence of the FMR1 premutation is no more frequent in children with academic failure than it is in the general population.