Professional development (PD) for graduate teaching assistants (GTAs) has been repeatedly emphasized as an essential component of future faculty training. Nonetheless, attempts to integrate PD programs into graduate curriculum are met with resistance from some stakeholders. The authors investigated stakeholders' perceptions of a novel GTA PD program implemented in The Ohio State University (OSU) Center for Life Sciences Education (CLSE), which coordinates biology courses at an R1 institution. GTAs involved in the program reported an increased sense of preparedness to teach, felt well-supported in their teaching, and critically reflected on their own teaching. This article describes program improvements based on feedback from this study. Although the independent PD course portion of the program always had a menu of developmentally appropriate activities for novice, midcareer, and veteran TAs, the CLSE made those options more transparent with group-specific syllabi and planning sheets that clarify the activities' relevance. The findings, TA PD resources, and ideas for future directions for the OSU CLSE TA PD program provide valuable guidance for other institutions seeking to provide quality ongoing training for GTAs.