In the article, the concept Ivanushka-durachok is considered as a national precedent name. The national-cultural significance of the concept is proved based on the opinion of predecessors. The deformations of the axiological paradigm of young Russian speakers are exemplified by this concept, modifications in its existence are fixed overtime. It is argued that the change in the semantics of the concept Ivanushka-durachok is explained by the development of the linguistic consciousness of native speakers over the past 40 years. In the course of the research, the psycholinguistic methods and the methods of corpus linguistics were used. The dynamics of the evaluative value of the precedent concept Ivanushka-durachok is indicated. It is concluded that the axiological and semantic potential of the concept Ivanushka-durachok and its name has been deformed. Its assessment vector in the linguistic consciousness of the student changed from positive to slightly negative. It was found that most of the preschoolers and some schoolchildren do not know the hero at all, do not have any associations with him, poorly represent his character traits, do not remember the fairy tales in which the character participates, do not reproduce the plot collisions associated with the hero, do not have a complete (and some even partial) understanding of the actions and characteristics of the hero and his antipodes, his environment. This is evidenced by the results of an associative experiment, according to which the hero is still recognizable as a fairy tale and folklore character inscribed in the schoolchild’s world picture. However, he is not attributed as invincible, disinterested, kind, trusting in the will of God, savvy, fearless, generous, highly moral. The hero is perceived primarily as intellectually limited, unkempt and unengaging. According to schoolchildren, the character is not suitable for personal friendship. The author considers the simplification and transformation of Ivanushka-durachok’s assessment to be a mutation of the cultural code. The change of axiological emphasis exemplified by Ivanushka-durachok is assessed as a diffusion of national-cultural idiosyncrasy, its unjustified debasement. The results of the analysis can help to correct the work with fairy-tale and folklore texts in kindergartens and elementary schools, be used in the teaching methods of literary reading.