Some children fail to learn to read as easily, or in the same manner, as their peers. This creates a persistent educational problem and considerable heartache for the children themselves. Three major groups of children are to be distinguished: (a) Those in whom the reading retardation is due to frank brain damage manifested by gross neurologic deficits. In these cases there are clearly demonstrable major aphasic difficulties, and they are similar to adult dyslexic syndromes. (b) Those with no history or gross clinical findings to suggest neurological disease, but in whom the reading retardation is viewed as primary. The defect appears to be in the basic capacity to integrate written material and to associate concepts with symbols. (c) Those cases demonstrating reading retardation on standard tests but in whom there appears to be no defect in basic reading learning capacity. These children have a normal potential for learning to read but this has not been utilized because of exogenous factors, common among which are anxiety, negativism, emotional blocking and limited schooling opportunities.
Failure to distinguish between these major types of reading disability leads to confusion and inadequate diagnosis; children of the third group may be (mistakenly) considered unintelligent, careless or even mentally retarded.
Estimates of the percentage of children handicapped in this way differ from country to country but range from 5 to 20%: boys outnumber girls 3 to 1. Learning disabilities have been described as the most pervasive educational problem in the USA.