I've seen this sentence on a website " I have been going to graduate school at USC".
what is the difference between that sentence and these two: " I am going to graduate school at USC" or "I have been graduating school at USC"?
There's no real difference. They are all wrong. CB
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The only scenario that comes to mind which would make 'have been going to' correct is one in which the student had intended to graduate but was prevented from doing so by circumstances, and this same sequence of events occurred repeatedly over many years. He might say, jokingly, "I've been going to graduate for years". It's not something you would hear said very often.
CJ