Okay, I exaggerate but I always liked titles that were full of hubris, so sue me. Anyways...
Guys will look/stare/glance/whatever at girls they have a crush on. They may be doing other things, like avoiding the teacher's gaze, but the attention is pointed at the object of their infatuation. What I've realized however, is that the cause and effect actually goes the other way!
Now maybe, this is old news, but its news to me. It just made so much sense after filtering through all the girls I've been strongly attracted to and not. Now the initial gut attraction is important as it grabs the attention. However if the attention isn't sustained, the 'crush' doesn't occur.
For example, in my english course we sit into a circle. On the first day, there was two girls I was attracted to just on looks, whatever. I became somewhat infatuated with one girl but not the other, why? One girl sat diametrically opposed to me in the circle, one sat to my left just outside my peripheral vision. Guess which one?
Well, after discovering the secret of this and thus realizing that it wasn't fate or anything extraordinary, I simply didn't look at her so much, and she changed her seat, and now she's just a another chick in the class.
BTW, all my high school crushes either sat somewhere in front of me in a class, or had a lead role in a drama club production I was in.
"Out of sight; Out of mind"