The topic of this master's thesis is the development of phraseological proficiency during Slovenian high school education. In the first section, I present the findings of the analysis of the Slovenian language curriculum in high school education and existing textbooks. The analysis attempts to outline the objectives of developing phraseological proficiency set by the curriculum, compare their implementation in textbooks, and present the content and methods by which their implementation is intended. In the second part, the results of the survey are presented, which was carried out in four Slovenian high schools among first and fourth graders. The results show the relationship between knowledge and use of phraseology after primary school and after high school. Using these results, I try to determine the level of knowledge and use of phraseology among first and fourth year students, and compare my result with the results of a survey carried out in 1987, published in Kržišnik (1990a). My interpretation of the results partly points to how selected phrases have formally and conceptually changed.