In Taiwan, teachers’ curriculum design competence has been challenged since the implementation of the General Curriculum Guidelines of 12-Year Basic Education in 2019. Teachers’ on-the-job training has also been organized differently from plenary speech to hands-on workshops. The effectiveness of the latter was well-received, but how did it happen? Ethnographic data was collected from observing 44 cross-school teacher community workshops, 40 interviews, and numerous postings in online social media. Drawing from the concept of “matter of concern” of Actor-Network Theory, the study identifies five assemblages: be willing to receive, be able to receive, be willing to understand, be able to understand, and practice. These assemblages were enacted by heterogeneous actors such as peer speakers, practical language, teachers, handouts, stickers, papers, posters, workshop schedules, arrangement of tables, snacks, social media platforms, and the facilitators. This study shows that the knowledge that the teachers performed at end of the hands-on workshop has become “matter of fact” through multiple hands-on workshop practice. This study will also discuss the role of objects, the enactment of hands-on performance, and the effectiveness of on-the-job training.