In countries such as the United States and Canada, an increasing number of non-native English speaking graduate students work in the capacity of university teaching assistants. Over the past several decades, a number of communication challenges between non-native English speaking International Teaching Assistants (ITAs) and native English-speaking undergraduate students have emerged. Universities have responded by developing ITA education programs that aim to teach English for the specific purpose of university teaching. This paper examines how ITA education can provide ITAs opportunities for authentic practice and reflection of communicating in an instructional capacity. ITAs enrolled in an English course participated in a video-recorded clinical simulation -- a form of situated practice in which individuals engage with an actor who is trained to interact with all participants in a consistent manner. ITAs met with an actor-portrayed undergraduate student who is visiting their teaching assistant to express concern about a group project. ITAs met in small groups following the simulated meeting to reflect on the shared experience. Qualitative analysis demonstrates that the simulated context elicited both challenges to comprehensibility and the use of strategies by students and ITAs to manage miscommunication, while working towards mutual understanding of the students' concerns. Reflective discussions reveal how the ITAs evaluated approaches to communicating with a concerned student in an instructional context. Embedding clinical simulations in ITA education can provide opportunities for the situated practice of using language to communicate instructional decisions, and as a structured opportunity for supporting mutual understanding between ITAs and native English-speaking students.