In-service teachers need professional competences comprising different kinds of knowledge like content, pedagogical and pedagogical content knowledge. In Germany, these different kinds of knowledge are taught by different scholars who hardly ever collaborate and in different semesters across the course of their studies. Thus, it is often left to the students how to construct bridges across learning boundaries between content knowledge and pedagogical content knowledge. As a result, the danger that knowledge learned at university level is not sufficiently coordinated, connected and integrated is high. The project "ProfaLe" is addressing this particular problem of boundary crossing within the university teacher training program in Hamburg. Here, interdisciplinary and strongly connected learning opportunities between courses of content knowledge and such of pedagogical content knowledge were designed, field-tested and finally evaluated. The design of such cross-domain learning opportunities poses challenges: First, on a structural and organizational level forms of cooperation among members of different domains or even faculties had to be developed and established. Second, different domains where either content knowledge or pedagogical content knowledge has to be learned often follow quite different objectives and teaching methodologies. We have addressed both challenges by the development of what we call "boundary objects". These are characterized by the fact that they a) are used both in the scientific and in the didactic domain, and/or b) have inscribed traces of these two disciplines in themselves. Subject-specific methods and operations, the didactic-methodical organization of teaching, subject didactic theories as well as materials for students’ learning can all be modelled as “boundary objects”. For example, classroom products such as written interpretations, classroom assessments or recordings of students’ talk in class can become "boundary objects" in the sense of "student material from the subject classroom", because this material bears traces of both disciplines (technical content as well as the learners' handling of these content). In the course of teacher education these traces have to be repeatedly separated and re-joined in order to allow for a more integrated acquisition of different kinds of knowledge. Taking the subjects of German and mathematics as an example, our presentation will demonstrate a) possible forms of structural-organizational interconnections of scientific and didactic learning opportunities (e.g. accompanying seminars, tutorials) and b) corresponding forms of the "inner" organization of interconnecting learning opportunities through boundary objects.

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