Perturbations that occur at each structural and functional level of the language with children who suffer from mental deficiency vary and influence the whole system of language acquisition at different degrees within this category of children. Language acquisition with mentally disabled children needs following a special methodology based on concepts and research results aimed at the disclosure of both the structure of the mental deficiency and certain specific manifestations. Both of them result from the neuro-physiological processes within the structural and functional levels of the language.