This study aims to provide insights in the professional development (PD) of teachers about to teach Computational Thinking (CT) in Danish K-9 schools, within the context of the potential subject Teknologiforståelse (Understand of Technologies). CT is defined as the ability to comprehend, question, and contribute to the impact of technologies in our society, hence complying with the legal mission statement of Danish public schools. The broad perception of CT challenges a widespread misconception among teachers and laymen, that CT is limited to programming and thus reserved specific careers. As observed in a review of international studies, Danish teachers seem to suffer from low self-efficacy regarding their competencies in relation to teaching CT, which can be connected to the misconception of CT, leading to unrealistically high expectations of the technological pedagogical content knowledge (TPCK) required to teach the field. A thematic analysis of interviews with six central actors suggests that the misconception leads to difficulties in teachers connecting CT to their regular subjects which, accompanied by low self-efficacy, tends to have a negative impact on their attitudes towards CT and be complicating their PD. Building upon the teachers existing PCK can help maintaining their professional identities but can also support the development of CT-related TPCK in connection to their regular subjects. The study suggests scaffolding as a framework for organizing the process of developing the teachers TPCK, as it focuses on lasting anchorage of the teacher’s capacity, by gradually assigning the responsibility of the PD to school-based peer-networks, thus removing the dependency of external experts. The scaffolding functions of recruitment and reduction in degrees of freedom can be met by inspirational conferences and plug-and-play lesson plans and positively affect the attitude of the teachers, by clarifying that the required TPCK are within their zone of proximal development. The functions direction maintenance, marking of critical features, and frustration control can be fulfilled by peer-networks and substitute non-lasting injections from external experts. Demonstration of state-of-the-art teaching can positively affect the attitude of the teachers by modelling the desired outcome and normalize their expectancies of their TPCK, while training it in relation to CT and should therefore, accompanied by reflections, be a recurrent element in the PD of the teachers.