Intractable shortages of science, technology, engineering, and mathematics (STEM) teachers have prompted international policy efforts to recruit career changers to the profession. This research determines the significant influences on career changers' decisions to pursue or pass on STEM teaching careers. Surveys completed by 91 career changers from Queensland, Australia, were analysed with Best-Worst Scaling (BWS) methods and Margaret Archer's theories of reflexivity to establish the relative importance of factors influencing career changers' deliberations on a STEM teaching career. The social impact of teaching was the most influential factor for career changers considering STEM teaching. Career changers who pursued the profession were also influenced by past teaching experiences and feelings towards STEM subjects. Conversely, career changers who decided against STEM teaching indicated their personal traits and life circumstances might not suit a teaching career. These findings offer implications for research and policy aimed at recruiting career changers into STEM teaching careers.