Learning disabilities (LD) imperil children's intellectual development and emotional health. Past attempts to associate LD with anomalies of cerebral organization have focused on severe reading deficiency (dyslexia). This research concentrates on children with LD in subject areas other than reading (non- dyslexics). The major hypothesis is that advances in right hemisphere function observed in normal children at about age 10 reflect maturation of neural substrate. These maturational processes are hypothesized to be attenuated in non-dyslexics. Four studies are proposed. Study 1, the main study, compares two LD groups: dyslexic and non-dyslexic boys, ages 8-12. They are given a wide variety of tasks on which adult patients with lesions of the right hemisphere are more impaired than those with lesions of the left hemisphere patients differ in types of error. Dyslexics are predicted to resemble left hemisphere patients and non- dyslexics to resemble right hemisphere patients in performance on these tasks. Moreover, since maturation of the right hemisphere is compromised in non-dyslexics and not in dyslexics, an age by group interaction is predicted in which the advantage of dyslexics on these tasks is greater after age 10 than before. Study 2 uses normal boys ages 7-13 to demonstrate that the developmental curve for these tasks is inflected at age 10. This would be consistent with a maturational interpretation of interactions between age and group in the main study. Study 3 is a questionaire study of the dyslexics and non-dyslexics in the main study. Geschwind and his colleagues have suggested a relation between LD and abnormal slowing of left hemisphere development in the fetal period. The studies supporting this hypothesis have associated LD with a large set of biological markers, including left handedness and disorders of the immune system. The hypothesis that non-dyslexics have right hemisphere dysfunction (and relatively normal left hemisphere function) implies that these markers should be found at lower rates in non- dyslexics than in dyslexics. Study 4 is a retrospective study on children evaluated over a ten year period as in need of special educational services. This is an attempt to corroborate the results of the main study with longitudinal data.