I think in many of these cases, the teacher is still in her 20's, and not that much older than the boys they sleep with. These women are younger and more immature than the teachers of prior generations. You'll occasionally have the teacher in her 30's or 40's do this, but for the most part it's the younger teachers that get infatuated with the strapping 17 or 18 year-olds.
"The best kind of pride is that which compels a man to do his best when no one is watching."