As teaching assistants (TAs), graduate students are often the primary resource in a classroom and serve as the communication gateway between students and instructors. Importantly, they may later become college-level instructors whose primary teaching experience was gained as a TA. Historically there is an assumption that content mastery solely is correlated to teaching success, and, as such, geoscience graduate students typically receive inconsistent and often inadequate pedagogical training. Additionally, the majority of a TA's responsibilities are frequently unrelated to teaching. In response, and following an assessment of graduate student needs in the Department of Geological Sciences, we have (1) initiated a developmental program on teaching and learning and (2) implemented an "Instructor-TA Agreement" to improve communication between course instructors and TAs. To expose graduate students to research-based teaching strategies and cultivate a community of engaged educators, we have initiated a program of workshops that extends skills development beyond the annual TA training session. The workshops are developed and led by graduate students and include topics such as effective questioning; facilitating discussion; fostering an inclusive classroom; and teaching in the field. By taking advantage of existing weekly graduate student seminar timeslots, the workshops have an attendance rate nearing one third of the current graduate student population, significantly greater than the number of TAs per quarter. The departmental "Instructor-TA Agreement" serves at the least to outline in writing the course-specific responsibilities of the TA, and, more substantially, encourages the instructor and TA to discuss potential opportunities for the TA to gain teaching experience, such as through creating a problem set, facilitating an in-class exercise, or delivering a lecture. Our efforts are leveraged by the rich resources of Stanford's Vice Provost for Teaching and Learning, which include university-wide workshop materials that we have modified specifically for the geosciences.