The article presents the results of a comparative study of grammatical structuring and the construction of a coherent utterance in younger schoolchildren with general speech underdevelopment and mental retardation in comparison with the norm. A significant similarity in manifestations and the presence of specific features are shown. The predominance of the deficit of semantic programming in the case of mental retardation and the difficulties of semantic programming, serial organization and lexical formulation of the utterance in the general speech underdevelopment was revealed.