<p>STEM graduate teaching assistants (GTAs) are responsible for teaching many undergraduate students. Yet, graduate teaching assistants typically receive limited formal pedagogical preparation. The reasons for this lack of professional development are sometimes external to the GTAs themselves (e.g., time or monetary cost to participate, few training opportunities offered by departmental leaders) and sometimes internal to the GTAs (e.g., their intrinsic desires or motivations to participate in such trainings, particularly if trainings are voluntary). In this study, we focus on those internal (motivational) reasons for the engagement, or lack thereof, of GTAs in teaching professional development. In particular, we used Self-Determination Theory as an analytical framework to explore GTAs’ motivation to engage in teaching professional development (TPD) programs to support their instructional practices. We conducted a scoping review of the literature with the purpose of identifying key features or characteristics of GTAs’ perceptions of their psychological needs for teaching, including competence, autonomy, and relatedness. This review identified 82 articles, published from 1989 to 2024. We found that GTAs tended to express high perceptions of instructional competence and variable perceptions of autonomy to make decisions around their teaching. This review also found common supports and thwarts to the development of GTAs’ positive perceptions of their psychological needs. TPD programs appeared to generally have positive impacts on GTAs’ perceptions of teaching competence, autonomy, and relatedness, which leads to a potential outcome of further engagement in TPD programs. Common thwarts we found were when GTAs taught courses where supervisors emphasized consistency among course sections, had unclear expectations, limited feedback on their instruction, or weak relationships with teaching colleagues. This review has implications for future research to address the development of GTAs’ positive perceptions of teaching autonomy and relatedness, leading to more engagement with TPD programs, and better instructional outcomes with undergraduate students.</p>