I'll put my .02 in your cup, to hopefully save you from many counterproductive ideas. There are no right or wrong ideas; it's a matter of what works, and what you accept into your mind. Bear in mind as you read this that this comes from my world. Your world may be different. I have to approach girls; Brad Pitt has to avoid crowds of girls!
1. In my experience, talking about class goes nowhere. Your grades do not "DHV," nor does showing her how much smarter you are than she is. The fact of the matter is that you were talking about facts rather than engaging her emotions, and to a woman, that's like having a speech impediment.
2. If a girl likes you, she won't let you go like that without securing a means of talking to you again. It works the same way as never asking her name; she'll ask you! If you were a girl who gets constantly hit on, gives out her phone number to some guys just to get rid of them (and doesn't pick up), and has no shortage of guys entering her life, what does your situation look like from this perspective?
3. Never wait. Read this
http://www.seduction.com/blog/call-her-today/