  Graduate Teaching Assistants (GTAs) are key partners in the education of
undergraduates. Given the potentially large impact GTAs can have on
undergraduate student learning, it is important to provide them with
appropriate preparation for teaching. But GTAs are students themselves, and not
all of them desire to pursue an academic career. Fully integrating GTA
preparation into the professional development of graduate students lowers the
barrier to engagement so that all graduate students may benefit from the
opportunity to explore teaching and its applications to many potential career
paths. In this paper we describe the design and implementation of a GTA
Preparation course for first-year Ph.D. students at the Georgia Tech School of
Physics. Through a yearly cycle of implementation and revision, guided by the
3P Framework we developed (Pedagogy, Physics, Professional Development), the
course has evolved into a robust and comprehensive professional development
program that is well-received by physics graduate students.
