The article examines the stability and success of ideas within pedagogical discourses. Why do certain ideas attract actors and how does change come about? These general questions are dealt with through considering the example of the swift spread of an interdisciplinary idea, "arbetsområde" (translated to "spheres of work") in the process of a Swedish national curriculum reform 1966-1967. How did it manage to become such a central concept in the curriculum? The article uses the concept of the boundary object in order to understand the popularity of the "spheres of work" concept. Boundary objects have normally been used to explain the rigidity of science, and how the heterogeneity of different actors normally involved in the production of scientific knowledge can be coordinated and result in generalizable findings. However, lately, they have been applied to the field of curriculum studies. In this study, a boundary object pinpoints the fact that curricular solutions can be about coordinating different types of actors with different stakes in the making of a curriculum.