I've been using the following script a lot and it has worked for me pretty well. It is not the most efficient way of picking up girls, but I find it to be comfortable and relatively risk free.

First I try to sell myself as a fun/exciting/friendly guy in class by talking to everyone. I ask people about their weekends and their interests while telling stories about myself. I usually joke around and try to stay positive. Once I get the girl I'm interested into the group I pass around my phone and get everyone to input their numbers and suggest everyone else exchanges numbers as well so we can share lecture notes/study together.

One day I text the girl to share notes or study together and ask her to meet me either at the library or a coffee shop nearby. If I sold myself correctly in the first part and established enough rapport with her she will agree to meet. If not then I either work harder at building rapport and try again, or I just ditch the whole plan and go direct.

Once I agree on a place and time with the girl I call my group of friends and get some of them to study with me or hangout in the same place I'm meeting the girl. My female friends are pretty good looking and my guy friends are very nice down to earth. Usually I can get at least 2 people to show up. Most importantly my friends are very welcoming and active socially, so they make the girl feel like she is part of our group.

The girl gets there and I introduce her to my friends and usually the atmosphere is very friendly/fun while I copy the notes or I study with the girl.

Next class I tell the girl that my friends thought she was cool, and then we talk about my friends some. I apologize for not inviting her to go out with us that day and promise that I will invite her next time.

At some point later I call the girl and tell her that my friends are getting together, and tell her I'll pick her up. I noticed that girls tend to flake less if you call them at this point. We go hang out with my friends, and then it should be pretty easy to isolate and escalate. I've had times when I would go and pickup two different girls to hangout with my friends, and then going with the path of least resistance.

If a girl resists your advances when you hang out with your friends you at least get a new addition to your friend group.