The congenital lesion population provides an excellent forum to investigate the issues of innate specialization and plasticity. Effects of early lesions on left and right hemisphere function reflect both the cognitive process under study and biological/neurological factors of lesion parameters and hemispheric maturation rates. In general, toddlers with both congenital left and right lesions show mild to moderate delays in language acquisition. School-age children with left hemisphere lesions have more problems with language and language-based academic skills than those with right hemisphere lesions, but the problems are subtle and do occur in both groups. This pattern stands in sharp contrast with the adult, who shows striking language deficits with acquired lesions only in the left perisylvian region. Thus, there is evidence in these studies of the immature nervous system for both innate specialization and plasticity, as well as a right hemisphere contribution to language acquisition and verbal cognition.