Plot hole: During Season 4, at Graduation, Andy informs Jack that she is 'deferring Harvard for a year' and going back to Italy instead, as she is happy there. Therefore, it makes logical sense that we never see Andy's character in all of Season 5, when all the other major characters ended up in Boston together. But it doesn't explain Season 6, when Andy should have been back in Boston attending Harvard University. It isn't likely she would have jeopardised her education and deferred a prestigious college like Harvard for more than a year (they probably wouldn't allow it); and if she was, in fact attending Harvard in Boston during Season 6 and she was such good friends with everyone, surely she would have hung out with them at times! Everyone else did. It doesn't make logical sense that Andy was attending college in Boston along with everyone else that year, but they never saw her at all. And they never explained her absence at all in the scripts. Plus the fact that in the Series Finale, she is at Mass. General in Boston furthering her medical training; implies she did indeed attend Harvard for her undergraduate, Pre-Med education.