In the current paper, we present an analysis of a case study in which we have followed Swedish primary teachers who voluntarily began using translated Finnish curriculum materials, i.e. a textbook and teacher guide, in order to reform their mathematics teaching. The multifaceted data, consisting of questionnaires, interviews, protocols from collegial meetings and classroom observations, were gathered during the period 2010–2014. The analysis of the interplay within this cross-cultural setting reveals the special characteristics and the challenges existing in practice. Both the experienced and inexperienced teachers offloaded a great deal of their agency to the materials in order to become familiar with the ideas they mediated. Yet, the lack of a clear rationale behind the organization of the materials, as well as the suggested activities connected to taken-for-granted features of the Finnish teaching tradition, made fruitful interaction problematic. The changes teachers made in their classroom practice were tightly connected to the support offered in the materials, without which the teachers abandoned their new classroom patterns. Based on the results of this study, we suggest a number of general aspects that we regard as important to consider when implementing curriculum materials developed within another cultural-educational context.