I've already recapped the bizarre episode in which Blair takes the LSAT after studying for one night and somehow doesn't completely blow it. I keep forgetting, though, that Blair actually went to law school. Presumably she drops out when she becomes the Eastland headmistress at the end of the series. Of course, given the amount of time she spends studying when she's in law school during season nine, maybe Langley Law just isn't all that rigorous.
Our first opportunity to enjoy Blair in the law school environment comes in this episode: Rumor Has It that Blair is hooking up with one of her law professors. It's a pretty heavy episode, actually, and is a great example of how Blair's character truly grew throughout the series.