The past decades have seen an increase in the enrollment of foreign-born students in U.S. STEM (Science, Technology, Engineering, and Math) graduate programs. This paper investigates whether having a foreign teaching assistant (TA) in a STEM class affects the outcomes of U.S. undergraduate students. I consider both subjective outcomes (the median evaluation scores) and objective ones (the students' course outcomes). I use administrative data from a large public university where TAs are conditionally-randomly allocated to classes. I find that TAs from countries where English is not the language of instruction receive between $0.24$ and $0.52$ points lower median evaluations scores (on a five-point scale) compared to their native-born counterparts, conditional on the course type. However, being taught by a foreign TA does not have a significant impact on the students' objective course outcomes, such as grades, STEM major declaration, and STEM graduation. These findings suggest that evaluations of teaching for foreign TAs should be used with caution as they might not be a clear reflection of teaching quality.