I don't recall it being specifically stated anywhere. Seniority might make sense -- say, Dumbledore center, next most senior on his right, secondmost senior on his left, lather, rinse, repeat -- but in that case, Doug, as the newest instructor, wouldn't be right next to Snape. It may just be "find an empty seat."
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Big Brother is watching you. And damn, you are so bloody BORING.
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Big Brother is watching you. And damn, you are so bloody BORING.