Slow development of the expressive language (SELD) a delay in the use of words associated to the normal understanding, is characteristic of a small proportion of children that later is the normal use of the language.

Dyslexia is an important subject in the development of the boy, since it approximately affects 5% of the population (in the western world). In essence one is an upheaval by which the children do not reach the linguistic competitions of reading, writing and agreed spelling with their intellectual capacities. The Dyslexic children show a series of differences in their development of the language, upheavals of the speech of subtle errors of pronunciation of the difficulties to find words. The more common phonological difficulties are the limitations of the verbal memory in the short term and the phonological conscience. These children usually have long term difficulties with the verbal learning like the months of the year, to learn the tables, end of 1980 the hypothesis of the phonological deficit has become the dominant explanation. The difficulties in the initial, basic joint and the acquisition of phonological abilities basic blocks of construction mean that the dyslexic must invest too many resources in only facing the basic concepts instead of acquiring new data or abilities. The early identification allows the children to receive aid before they fail.

Delay in the atypical development of the language can be a autism diagnosis, and the regression of the language can indicate serious developmental like the syndrome of Rett. the insufficient development of the language also accompanies to delays in the general development, such as the found ones in the syndrome of Down