Ye, it might be a issue,however Chinese students are everywhere, it really depends on ur personality, if you are social then u will find a way to improve English, u r right, it doens't matter.
i m saying that maybe you dont even have any native speakers in your class...
even if you do... think about it...
you are sitting there... other Chinese students come into the class; they 'll prefer to sit next to you...
what are you gonna do? tell them to go away?
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i guess i m too negative on Columbia's master program... hehe
but anyway, you should send their current students an email to ask for more information... their comments are more valuable...