The key role of teachers has been widely acknowledged in education reform and pedagogical innovation, and there is no exception in STEM education. This paper documents affordances and tensions in the implementation of STEM applied learning programme (ALP) through investigating school leaders and teachers' sensemaking of the new approach. Attending to both the individual processing and the social interactive work with issues of coherence, sensemaking theory provides a theoretical framework for analysing school culture and resources and connections between actions and understandings of school leaders and teachers in the programme. In this qualitative case study, semi-structured interviews and focus group discussions were conducted with three school leaders and three teachers from two Singapore secondary schools to identify their prior understandings, shared interaction and interpretations during the practice. The findings provide some insights into implementations of STEM in schools and professional development.