Graduate teaching assistants (GTAs) significantly contribute to the learning and experiences of undergraduate students. Thus, supporting and enhancing GTA pedagogical knowledge and competencies can improve the learning experiences of undergraduates. Towards this goal, a discipline-specific pedagogical professional development program was created for GTAs in the Faculty of Engineering at a Canadian university. This case study explores the perspectives of participating GTAs, including how they engaged in learning about teaching, what they learned, their emerging educator identity formation, and the challenges they faced during the program. Situated learning theory informed the analysis of participant interviews and focus groups. Findings indicate that GTAs appreciated the situated and embedded nature of the program, reporting limited prior familiarity with pedagogical tools and practices and their application. Results also highlight the need to align GTA roles and responsibilities, providing opportunities to put their learning into practice with the pedagogical knowledge they developed in the program.