The article is devoted to the problem of the formation of language competence of junior schoolchildren in the process of prevention and correction of disorders of written speech in them. In children with persistent disadvantages of oral speech at phonetic - phonemic underdevelopment (PPU), general speech underdevelopment (GSU), systemic underdevelopment of speech (SUS) at delayed mental development (DMD) deficiencies of pronunciation of sounds and phonematic processes are observed. In addition, insufficient formation of lexical and grammatical generalizations, cognitive and communicative functions of speech are characterized for children with GSU, SUS at DMD. These shortcomings in the development of various components and functions of speech as a system make it difficult for such children to form the ability to distinguish and, in accordance with the rules, use different units of language. The article reveals the directions and features of the formation of language competence of junior schoolchildren. The work of the formation of knowledge about language units (sound, letter, syllable, word, combination of words, sentence, text), parts of speech (noun, verb, adjective, pronoun, preposition, adverb), combination of words and types of sentences is considered. The formation of skills of speech analysis and synthesis (phonemic analysis and synthesis; analysis and synthesis of syllable; analysis of sentence by words, synthesis of sentences from words), skills of elementary morphological analysis of parts of speech, morphemic analysis of a word, elementary syntactic analysis of sentences is highlighted. The formation of language competence of children with PPU, GSU, SUS at DMD should improve the effectiveness of correctional and developmental work on the prevention and overcoming of disorders of written speech in them. The formation of this competence will stimulate manifestations of cognitive activity in the study of native language, will contribute to better awareness of schoolchildren about compliance with language norms and rules, more conscious and controlled implementation of written tasks.