Sustainability efforts, such as environmentally friendly and resource-saving production, the efficient use of an energy management system, or the trade-off between renewable and fossil fuels, are becoming increasingly important for companies (cf. Cooremans & Schönenberger, 2019, p. 264f.). To address these efforts, different occupational disciplines, such as technical and management disciplines, need to combine their knowledge and expertise. For this, interdisciplinary skills are becoming increasingly important, as different occupations with different areas of expertise need to communicate with each other. One solution to foster interdisciplinary skills early on is to establish these skills during vocational education and training.

In Germany, a dual system of vocational education and training systems offers students the possibility of an apprenticeship. During this apprenticeship, students acquire job relevant skills based on occupation specific curricula. However, these curricula currently lack the promotion of interdisciplinary skills (cf. Sloane et al., 2018, p. 13). While business managers and technicians have to work together on a daily basis in most companies, German schools within the dual system of vocational education and training currently do not prepare their students for this task.

This study looks at the educational programme work of an interdisciplinary educational team of teachers from both business and technical vocational schools. An interdisciplinary team of teachers was formed to propose learning scenarios that are anchored in a curriculum to promote the interdisciplinary skills of students from business and technical vocational schools.

Following the design-based research method, a research portfolio on the interactions between teachers from the interdisciplinary educational team offers insights on interdisciplinary skills at the teacher level. First, the teachers themselves benefited from the interdisciplinary collaboration. Pedagogical experiences were exchanged, new learning and working strategies were developed, and the repertoire of teaching materials expanded. Second, challenges were identified regarding the coordination of course content within the apprenticeship. This includes course contents that are relevant for both business and technical occupations. Teachers had to identify common curricular links and consider their inclusion in the schools methodological and annual didactic planning as well as the concrete design of learning scenarios and the development of teaching-learning arrangements (cf. Sloane, 2021, p. 230). Another challenge that was identified relates to the different experiences, attitudes, and assumptions of teachers, partly due to their occupational discipline (cf. Krainer & Smetschka, 2014, p. 72). This creates barriers that make collaboration more difficult (cf. Claus & Wiese, 2021, p. 280). However, these barriers can be addressed systematically.

Following the framework of Claus & Wiese (cf. 2021, p. 282), the teachers showed "initiative for exchange" as they willingly and actively participated in the interdisciplinary exchange within the teamwork. They also intuitively used "target group-specific communication" to foster the interdisciplinary teamwork. Both mechanisms helped in reducing barriers. Regarding “integration of knowledge” and "reflection on one's own discipline" the teachers showed more difficulties. Here, the teachers appear to need additional support in understanding the other occupational discipline as well as acknowledging more strongly their own discipline.

Applying a design-based research approach, a research portfolio was produced following five teachers over a six-month period. Three business and two technical teachers continuous-ly took part in the coordination meetings to jointly plan the lessons. In total, twelve coordi-nation meetings between business and technical teachers were followed during the meetings. Of the twelve meetings, nine took place online and three in person. Design-based research in general is characterised by an interaction between science and practice with iterative development cycles (cf. Euler, 2014, p. 15ff.; cf. Jenert, 2023, p. 11f.). On the practical side, this type of field research aims to design a prototype, which in this case is expressed in concrete implementation ideas to promote interdisciplinary understand-ing between business and technical teachers. Accordingly, the aim of design-based research in the context of science-practice interaction is to mutually develop an understanding of the problem and the solution-related ideas of the other party (cf. Jenert, 2023, p. 14). The starting point is an empathetic attitude of science and practice with the aim of adopting each other's perspectives (cf. Jenert, 2023, p. 16). Sloane becomes clearer here and presents three concrete forms of mutual perspective-taking between academia and practice: "Three responses are possible referring to inter-subjectivity: empathy, textual reality and the second-person perspective" (Sloane, 2017, p. 11). Based on design-based research, a research portfolio was used to observe the exchange processes between the business and technical teachers. The research portfolio is characterised by mutual documentation and self-reflection. A research portfolio has already been used by several authors in the context of design-based research (cf. Frehe-Halliwell, 2015; cf. Volgmann, 2023). The documentation serves to present the knowledge gained (cf. Gerholz, 2010, p. 72) and thus creates transparency and traceability. In addition, the documentation goes far beyond the understanding of a progress report. Rather, the aim is to document or analyse the overall process (cf. Breuer, 2003). The goal-orientated reflection of the overall process goes hand in hand with documentation and observation as self-reflection is about analysing the observation (cf. Dörner, 1994, p. 202). Self-reflection therefore means, for example, making perception and thought processes the object of observation (cf. Dörner, 1994, p. 202). Since subjective impressions are often documented in the research portfolio, it is important to mirror the self-reflection and documentation to the technical and business teachers at each meeting. This should legitimise and confirm the impressions.

Topics such as energy management, which are becoming increasingly relevant in everyday working life from a business and technical perspective, need to be considered early on in vocational education. This study shows the opportunities and challenges of collaboration between business and technical teachers to realise joint teaching units for business and technical students which so far is missing in curricula of vocational schools. As a result of the joint work on the educational programme, it became clear that before teaching could be initiated with the aim of promoting interdisciplinary skills, the teachers themselves first had to deepen these skills. According to Claus & Wiese (2021), the following areas are required: "initiative for exchange", "target group-specific communication", "knowledge integration" and "reflection on one's own specialist discipline". However, it is not only the interdisciplinary skills of teachers that are improved in this respect. This partnership can also generate innovative ideas for lesson design, new methods, and authentic teaching units. The aim of this study is to establish a long-term partnership of teachers to promote out-of-the-box-thinking. But also, to gain insights into the conditions under which teams with different occupations can work together. After all, there is no one right answer to many challenges and crises; it is always a matter of weighing up many perspectives and options. And this is best done during training.

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