While there exists a considerable body of research focusing on international teaching assistants' (ITAs') linguistic, sociocultural, and instructional challenges, less is known about the successful developmental trajectories of this group of international educators of American students. This research aims to fulfill this research gap using a case study approach (Yin, 2003). The study involved ITAs from STEM majors in six collaborative mentoring sessions prior and upon video recording of three lessons taught by the ITAs to undergraduate students. The mentoring sessions were designed to facilitate ITAs' reflections on their teaching with the use of structured protocols to help guide the discussions. All the collected data were analyzed using content analysis (Miles & Huberman, 1994). The results highlight the incidents of professional growth exhibited by the participating ITAs during their actual teaching. This study also tracks the ITAs' reflections on teaching through the mediational dialogues (Vygotsky, 1978) with the mentor. Finally, the paper discusses lessons learned through launching a mentoring project with a group of ITAs.