Universities often require incoming graduate teaching assistants (GTAs) participate in a Teaching Assistant Orientation (TAO), though the scope and content vary. TAO at the University of South Carolina, provided by the Center for Teaching Excellence, is an intensive, mandatory, one-day event at the start of each semester. TAO provides information from campus-wide teaching-related policies and procedures, to campus resources for GTAs and undergraduates, to best pedagogical practices. Historically, TAO has been an in-person event; however in Fall 2020, the first semester of data collection for this project, TAO was moved online due to the SARS-CoV-2 pandemic. Recognizing online delivery of some TAO sessions allowed GTAs more freedom in personalizing their professional development (PD) based on GTA role, interest and concerns, a hybrid format has been used since Fall 2021. Beginning in Fall 2020, GTAs completed qualitative and quantitative surveys before and after TAO, at the semester midpoint and semester end. Data from the pre- and post-TAO surveys are presented. As motivations are complex and often influence one another, a cluster analysis was used to identify the relative roles and associations of GTAs' self-efficacy, excitement about their GTA role, and ratings of common concerns were considered via cluster analysis. This revealed distinct groups of GTAs with similarities in characteristics, teaching-related concerns, confidence and attitude toward teaching that otherwise would have gone undetected. A better understanding of the GTAs and their motivations could allow TAO organizers to provide and recommend specific sessions to GTAs in each cluster. These data also revealed which of GTAs' concerns were alleviated during TAO or persisted, suggesting germane topics for future PDs. This study allows us to better understand the diverse and complex needs of novice GTAs, identify similarities and differences between groups of GTAs and personalize the teaching-related PD offered and recommended during and after TAO.