Mental retardation refers to a condition in which a person's ability to learn and to function is more limited than others of the same age. During infancy and the toddler years, a child may be considered only a bit slow, although delays in development and in language and motor skills may be apparent. A diagnosis of mental retardation, however, is often not made until the child is in elementary school and has difficulty in mastering academic skills. Although children with Down Syndrome are mentally retarded, there are a number of other causes of mental retardation.