But for many students majoring in math or physical science (including one I married), the problem was distressingly common among both professors and teaching assistants. Their ability to communicate effectively was hindered not only by limited English-speaking ability but also by the lack of any pedagogical training for those who were occasionally pulled from their research or lab work to "teach" a class.
I don't fault the individuals but rather the institutions, including my alma mater. Back then, it didn't seem that students had any recourse. Perhaps now that is changing.