This chapter focuses on student teachers and their transformation of knowledge in boundary crossing between an educational context and a professional teaching context. The chapter reports on a design-based research project involving the development and test of a learning design aimed at facilitating this transformation of knowledge between two life settings: a first language course at the Teacher Education Program and a 5th Grade class in a public school. Using a framework of context levels, it explains how requirement characteristics of the respective life settings concretise the activities and the domain differently in the two settings. Examples are presented and discussed concerning how the resulting unity of requirement characteristics lead the students to enact their knowledge differently in the two settings, and how they transform and resituate their knowledge in attunement to this unity through a situated readiness. The chapter concludes by suggesting two possible design improvements to further support the students in developing situated readiness: by adding transparency and by supporting their awareness of the sameness and differences between the two settings.