This thesis names the Oxford School of children’s fantasy literature as arising from the educational milieu of the University of Oxford’s English School during the mid-twentieth century. It argues that J.R.R. Tolkien and C.S. Lewis lay the foundations for the children’s fantasy genre by introducing an English curriculum at Oxford in 1931 (first examined 1933) that required extensive study in medieval literature, and by modelling the use of medieval source material in their own popular children’s fantasy works. The Oxford School’s creative use of its sources produces medieval ‘afterlives,’ lending the Middle Ages new relevance in popular culture. This research directly compares medieval literature to children’s fantasy works by Tolkien, Lewis, and four other Oxford-educated children’s fantasy authors in order to reveal the genre’s debt to actual medieval texts and to the Oxford English syllabus in particular. The four authors are Susan Cooper, Kevin Crossley-Holland, Diana Wynne Jones, and Philip Pullman. This thesis situates the tendencies of medievalised children’s fantasy in relation to Lewis and Tolkien’s personal and scholarly convictions about the patriotic, moral, and aesthetic qualities of medieval literature and folklore. Building on the theories of Michel de Certeau, this thesis demonstrates how Oxford School fantasy produces new mythologies for England and argues that, as children’s literature, these works have an implicit didactic function that echoes that of the English School curriculum. This thesis traces the attempts of some Oxford School authors to navigate or explode generic conventions by drawing upon new source material, and contends that the structures and hierarchies that underpin the genre reassert themselves even in texts that set out to refute them. It suggests that such returns to the norm can produce pleasure and invite diverse reading, growing out of the intertextual associations of each new rewriting.