The aim of this dissertation is to investigate the language ideologies in the 2011 and 2021 detailed study programs of the modern Greek language course for secondary school (gymnasio) and their didactic implementation in the textbooks of the third grade of secondary school (gymnasio). The methods of content analysis and critical discourse analysis were used in combination in order to study linguistic ideologies about standard language and linguistic correctness, linguistic pluralism and the relationship between modern and ancient Greek. The analysis of the data of the two detailed study programs revealed the central role of the standard language in language teaching and its direct connection with linguistic correctness, the absence of other languages/language varieties and the derivation of prestige for the modern Greek language from the ancient Greek language in a continuity relationship. Also, the study of the teaching manuals projected the dominance of the standardized, correct, regulated form of the modern Greek language in teaching and highlighted linguistic ideologies related to the preservation of the correctness and superiority of the standard modern Greek language.