Physical education teachers and the programs that prepare them find themselves in the early part of the 21st century in a public policy environment that differs significantly from that of the 20th century. This policy environment is grounded in an ideology that postulates that schools and teachers, rather than social forces, should be held responsible for academic outcomes, and in turn, economic success. For the first time, physical education teachers are being held accountable for student learning in the same way as their classroom peers. Improving the effectiveness of teachers is seen as the primary mechanism for improving student learning. In discussing how teaching effectiveness has evolved, I describe a relationship among the process--product paradigm, the ecological paradigm, and a neo-ecological paradigm called the instructional core. The latter paradigm extends our understanding of teaching effectiveness in new ways by describing the dynamic and interdependent relationship among teacher, student, and content in the gymnasium. It has significant implications for the professional development of teachers and the conduct of teaching effectiveness research. I conclude by discussing why content is so critical to conceptions of teaching effectiveness.