This paper reports on a research-based mathematics curriculum program development project in Sweden, whose educational context is currently characterized by multiple reform initiatives. Current reforms include a repositioning of the teacher as central for students' learning, but also a trend toward initiatives and teacher resources that are more directive than has been the case in the past 30 years. Collecting data from multiple sources, such as teacher log books, lesson observations and feedback meetings, we build on input from 11 elementary school teachers trying out our materials, including student texts and a teachers' guide, during four trial rounds. We analyze how international research about curriculum programs and teachers' use of these programs are interpreted and operationalized within the Swedish context. In particular, the two research questions guiding the study are: (1) "How do Swedish teachers interact with and reason about the reform-based classroom practices promoted by the curriculum program?" and (2) "How do Swedish teachers interact with and reason about their use of a teachers' guide?" From our experiences in the Swedish educational context, we suggest the following contextual aspects to take into account when designing a curriculum program whose design is grounded in international research literature: characteristics of current classroom practices, teachers' role in classrooms, the level of explicit/implicit support teachers are used to receiving, and teachers' experiences using a teachers' guide.