First, if you're going to do it, you have to be prepared for the rumor mill. Even if you do it in a car (btw: are you f-ing kidding me? we're not in high school anymore), one of you will undoubted tell someone, who will tell someone else and soon everyone will know you slept together.
Second, if she's in your section, I would say no matter what, it's a bad idea, especially if your section is small. Unless both of you are the type of person who is fine with being at least on neutral terms the day after the break up, things could become uncomfortable.
And third, make sure that you're both on the same page. Essentially, if you're looking for nothing but a f**ck-buddy, make sure she has absolutely NO expectations of anything more. If you're looking for a casual dating relationship, again, make sure she's there too. This should go without saying for any relationship, but especially law school, where a bad breakup possibly caused from her wanting more from you in a relationship can exacerbate the two problems above.
LOL!!!!!- WHAT A RIDICULOUS ANSWER; Why is it this man's job to "make sure she has absolutely NO expectations of anything more"
If this girl gives it up to him without such a discussion she runs the risk its just sex to him- as it may be to her/ and if she wants more than it will be lesson learned...or not. "make sure she's there too"- why? Again why is this his responsibility? I assume she is an adult; he doesn't need to babysit her.