One potentially significant but little-examined opportunity for graduate students to acquire experience with discipline-based writing is to serve as a Graduate Teaching Assistant (GTA) for Writing-Intensive (WI) courses at universities that sponsor writing-across-the-curriculum and writing-in-the-disciplines programs. This chapter reports on one such well-established program in which over 100 GTAs each semester serve in a variety of capacities for WI courses in their own disciplines. The chapter features both qualitative and quantitative data demonstrating the success of the program. Voices of representative GTAs, combined with independently obtained survey data, show that multiple outcomes are achieved: Graduate students are engaged with discipline-based writing, graduate students are prepared for their future careers, graduate students’ discipline-based teaching ability is improved, and mentorships between graduate students and their supervising faculty develop—all of which add up to being much more than just a “grader” for a professor in a WI class.