JPlaya said:
It's harder since yall are spaced out and you have a teacher talking
Do some cold reading that requires the use of her hand.
Start passing notes back and forth and tell her you need to see her hand. Draw a picture on it.
After you've developed at least a little rapport, ask her if she's ticklish. Then find out if she's telling the truth.
Lightly hit her on the shoulder for whatever reason you or some other circumstance creates (her giving a wrong answer for example, saying something that leads her to say something you could accuse her of "hitting on you" for)
Really, there are lots of reasons you could playfully hit a girl, even if you are separated by 1 ft. or more
As you leave the room, walk in front of her and use your hand to guide her out of the room against her shoulder.
Same thing with entering the room.
Same thing when she's sitting down in a chair.
Be creative. You can find ways to use kino in class.
EDIT: And don't worry about the teacher. I've done all of this before, after, and DURING class and never had a teacher get on my case. I did have a teacher tell me after class he thought I was awesome. But that's as far as it went.
And another aside. You are in college to learn. Your GPA is a much more important thing than a broad you're probably not going to even have sex with. If you can't do well enough in the class to practice PUA skills and pay attention, DON'T stop paying attention. You're in freaking college. There are plenty of other much easier routes to go in that setting to pick up girls than in the classroom.