Paper is dedicated to the testing of the concept of "literacy," based on the questionnaire, carried out in the school year of 2018/2019 among the students of two secondary vocational schools in Vrsac, Belgrade and Grammar School in Vrsac (200 respondents). The primary hypothesis of the research was that detection and detailed study of high school students conceptosphere on literacy identify the fields to improve the teaching of Serbian as a mother tongue in secondary schools and the aim of work that, based on the collected and then processed data in analytical, cognitive and descriptive method, is to (a) isolate the dominant concepts of (non)literacy, (b) look at the tendencies of spreading and shaping the notion of literacy induced by the needs of modern life, and also that, in order to improve linguistic culture in all domains and all educational levels -- (c) point to the possibility of improving the teaching of the Serbian language as a mother tongue. According to results of the survey secondary school students experience literacy in the 21st century as a complex concept; from the one who is literate expecting linguistic knowledge, what are the basic, traditionally accepted parameters, and recognize illiteracy as the lack of ability to apply knowledge in the field of language. They also demonstrated that it is necessary to improve the efficiency of teaching approaches designed to improve functional literacy in a variety of communicative situations; increase the number of hours and exercises in the field of spelling, or nurture and acquire more comprehensive and knowledge in use and skills of different forms of literacy needed for managing in 21st century; more attention should be paid to including relevant language handbooks in teaching; more explicit, on frequent and more familiar examples to students, point to the advantages of knowing and respecting the linguistic norm, paving the way for a better linguistic culture and enrichment of the mother tongue.