I tend to instinctively recoil from the male teacher x female student trope. I think I'm just stuck at the exploitation and doesn't get the fantasy that others get (from either side). Somehow though, this one works for me.
I think it's because the relationship dynamics are more equal here. We see more from his point of view, and he's just about pathetic (lol) enough to be sympathetic. The girl is quite headstrong and holds her own with him, or at least she does a good job acting as such.
That and both of them really are quite pretty.