Abstract Metalepsis the transgression of ontological boundaries between narrative levels has attracted considerable scholarly attention, yet its particular uses within Young Adult (YA) fantasy fiction remain largely unexamined. This article argues that when metalepsis is realised through the diegetic act of reading, it enables YA novels to do something conventional literary criticism has long asserted but rarely demonstrated: to show, in the structure of the narrative itself, how reading assists adolescent growth. Working across three canonical YA fantasies Michael Ende's The Neverending Story (1983), Cornelia Funke's Inkheart (2003), and John Connolly's The Book of Lost Things (2006) and drawing on Klimek's tripartite distinction between descending, ascending, and complex metalepsis, the article develops a model in which the metaleptic transgression of narrative boundaries serves as a structural externalisation of the adolescent protagonist's internal developmental process. Each novel's child protagonist enters the act of reading carrying a specific unresolved confusion concerning identity, power, and emotional loss respectively and the metaleptic mechanism literalises that confusion within an alternative diegetic world, compelling the protagonist to confront and work through it. A further argument concerns the recursive, Möbius-strip structure shared across all three metaleptic forms: this structure mirrors adolescence as a developmental condition transitional, boundary-dissolving, and constitutively unfinished. Taken together, the three analyses suggest that metalepsis, reading, and growing up are not simply thematically aligned in these texts but structurally unified, and that this unity gives narrative form to what reader-response theory has long claimed but left largely abstract. Keywords: metalepsis, narrative theory, Young Adult fiction, adolescent development, reader-response, diegetic levels, Möbius-strip narrative, fantasy fiction.