A girl will laugh with you more, touch you more, make an effort to sit with you or find out where you are going out to (if its a fri or sat evening or something) maybe she will try and come along, or if I liked a guy I would prob text him or something just being friendly but making coversation. If you think she likes you she probably does because if shes a nice girl shes hardly going to be all over you in 2 seconds flat in the middle of the 6th form common room! I would just ask her if she wants to go out sometime (you said you liked her) if she says yes you will know she LIKES you LIKES you, and if she says 'well who else is going?' or 'wow yes ill tell my friends to come too' then she sees you as a freind, I'd ask her out somewhere, you stand nothing to loose and it sounds like she has the hots for you matey. PM and let me know how you get on or post it up here!