This study investigated the underlying disorder of certain children who may have normal or above-normal intelligence, yet fail to read at levels appropriate to their ages. Twenty-two poor readers and 22 normal readers were matched on sex, age (7 to 12 years), and IQ (94 to 130). Examination of school records revealed that many poor readers were characterized as having short attention span, being immature in perceptual ability, being hyperactive, being immature in fine-motor ability, and behaving antisocially. In this investigation, two letters were presented simultaneously. Subjects responded by pressing one switch if the letters were the same, and another if different. Reaction time was found to be longer for poor readers. In addition, reaction times increased during testing and decreased after a rest more for poor than normal readers. Main effects for age and IQ were present. Correlations between initial reaction times and changes were significantly different for poor and normal readers. The results were interpreted as support for a theory that certain learning-disability children respond to laboratory tasks with suboptimal levels of arousal. References are included. (AW)