Development of hierarchic organization in perceptual, symbolic and motor sequencing remains among the most important unresolved problems in developmental and cognitive psychology. Serial processing of verbal and nonverbal sequences and temporal organization in motor action and speech production are the neuropsychological functions most frequently implicated in a psychological explanation of academic failure in children of normal intellectual potential. The objectives of this proposal are to analyze the development of serial order in behavior by longitudinal and cross-sectional developmental studies. Serial organization and spatial abilities are contrasted throughout. Examination procedures emphasize sensorimotor sequencing of the fingers and arms, serial processing of perceived sequences, ability to translate between spatial and temporal coordinates, transfer of learning for motor sequences, and serial pattern learning. Studies emphasize sex differences, variations in maturational rate, differences of hand preference, and differences in the development of hemispheric specialization. Primary populations comprise normal school-age children. Children at risk for learning disability and selected adult populations augment the samples.