A group of 35 reading disable (RD) boys and 35 matched controls were studied over a two-year period in order to evaluate the validity of traditional hypotheses about the cause of serious reading impairment in preadolescent boys for whom the common disadvantages of economic privation, bilingualism, and emotional instability were absent. The popular hypothesis of perceptual deficit was not supported by the data, although the finding that most RD boys have a short-term memory deficit was affirmed. The most important new finding was that about one-fourth of the RD boys had serious difficulty in maintaining an efficient set to process and/or evaluate information, especially when that information was contained in oral speech.