Science, Technology, Engineering, and Math (STEM) departments around the United States depend on international teaching assistants (ITAs) as a significant source of teaching labor, particularly in lower level laboratories. This situation has largely been framed as a problem that stems from ITAs' English language proficiency. Research has reflected this framing by searching for the linguistic sources of the ITA problem. Applied linguists have pinpointed ITA prosody, discourse marking, and morphosyntax as being markedly different from native speaker norms and thus having significant effects upon listener comprehension and perception. Strikingly though, little attention has been paid to ITA-undergraduate interaction in the university classroom. This dissertation investigates ITA-undergraduate interaction in Introduction to Physics laboratory sessions at a large U.S. university. Drawing on Conversation Analysis (CA), the analysis provided shows that repair sequences are interactional sites where ITAs and undergraduates co-construct intersubjectivity, institutional identity, and interactional competence. To conclude, suggestions are made for improving ITA-undergraduate interaction in the university.