Undergraduates have complained for decades about their teaching assistants. If you attend a university, chances are excellent that you will have at least some classes where a graduate student will serve as the teacher.
TA’s are cheap and when they are teaching introductory courses, the professors don’t have to do it. And tenured professors love shirking that responsibility.
This is a touchy subject, but plenty of students have complained that they can’t always understand foreign-born teaching assistants. Teaching assistants of any nationality aren’t selected because of their teaching skills; they are chosen simply because they are in graduate programs. So there are plenty of inept home-grown teaching assistants, as well as those from overseas.
A study completed a few years ago focused on an interesting question. Are undergrads who take classes from foreign-born teaching assistants hurt academically? The researcher concluded that the grades of these students do suffer slightly.
You can learn more about the findings by visiting a blog called Pure Pedantry, which is written by a guy who is obtaining a PhD and medical degree.
An article in The New York Times three years ago also discussed what undergrads are up against when TA’s command of English is shaky.