Context. With the introduction of Computer Science (CS) into curricula worldwide, teachers' adoption of CS pedagogical content is essential to ensure the long-term success of reform initiatives. Continuing Professional Development (CPD) programs play a key role in this process. Unfortunately, adoption is seldom evaluated in CS-CPDs or CPDs in general. The result is a dearth of studies (i) modelling teachers' adoption of CS pedagogical content or (ii) investigating factors influencing the uptake of this new discipline. Both aspects are crucial to design and characterize successful CPD programs. Objectives. We thus propose the Teachers' Adoption of CS (TACS) model to investigate factors influencing the adoption of CS pedagogical content by teachers who are following a mandatory CS-CPD program. More specifically, the model proposes that contextual factors (e.g., age, gender, and general teaching experience), prior factors (e.g., experience, and CS perception), and acceptance factors (e.g., interest, and self-efficacy) may impact teachers' adoption of CS pedagogical content. Methods. The study included 180 grades 5 and 6 teachers (students aged 9-11) that were following a mandatory CS-CPD program. The CS-CPD program involved participation in three-day-long sessions distributed over the 2019-2020 academic year. In between sessions, with the support of instructional coaches in the schools, teachers were encouraged, but not required, to adopt the CS pedagogical content. Therefore, during the CPD, and employing surveys based on the TACS model, we evaluated teachers' adoption of the proposed content and investigated how the different factors influenced it. Results. At the PD-level, the results indicate that self-efficacy and interest queried during the CS-CPD are indicative of CS pedagogical content adoption. To shed more light on the relationshipbetween these metrics, a more in-depth analysis was conducted with n = 92 teachers whose responses could be matched between sessions. While interest relates to how teachers adopt CS pedagogical content overall, both interest and selfefficacy are necessary to ensure the likelihood of a specific activity being adopted. Finally, individual teacher characteristics appear to impact adoption, with teachers with low experience with Information and Communication Technologies (ICT) requiring onboarding, while middle-aged teachers require convincing to adopt CS pedagogical content. Conclusion. Three takeaways emerge fromthe study. First, the analyses confirm the foundation of the TACS model. Second, the findings establish the key role that interest plays in said model. Finally, the results support the relationship between the contextual, prior and acceptance factors on the adoption of primary school CS pedagogical content.
