1. If she is constantly making eye contact with you. (Not the WTF are you looking at kind though)
2. Non verbal contact, as in, if you tease her or flirt with her and she smacks you shoulder and playfully hits you. Or if she just touches you out of the blue, all doing these things without being engaged in conversation.
3. Next time you sit next to her look at how she sits. A womans shoulders act like an arrow and will point right at the very thing they are interested in... namely you.
4. If you guys are in the hugging stage, next time, instead of putting your arms up high near her ribs put them around her waist and pull her hips right into your own. It's called the slow roast, it's where your bodies are touching from toes to tits, and if she lets this happen and she holds it there, well that a pretty good indicator.
Since you are in school together, go right up to her after class and say. "You know your lucky to be in this class with me. Now you have somebody that actually knows what's going on and can help you get better grades. We should study together. (insert time, and place here) would be the best time for me." She'll be all over it.