This article introduces an empirical analysis of the potentials and contradictions of a "narrative playworld intervention" aimed at changing the pedagogical practices of a Finnish mixed-age elementary school classroom in spring 2004. In the playworld, students and teachers explore different phenomena by taking on the roles of characters from a story and acting inside the frames of an improvised plot. The analysis is based on an understanding of school as a historically and culturally formed activity system. The playworld, on the other hand, is understood as a collective imagined and materialized "figured world". The findings show that for the teachers, the main contradiction in the playworld was between keeping control and promoting student initiatives. For the students, the contradiction arose between the student role and that of agent in the playworld. However, the contradictions also created the main developmental potentials of the activity. That the playworld was not only a tool for transforming classroom work but a world in which to belong made it possible to sustain the activity and make it a regular part of classroom practices.