It's not different. It's just that men don't even want to imagine a male teacher "soiling" their precious 16-year-old princess of a daughter, but these same men can very easily imagine their 16-year-old son sowing his wild oats by having sex with any female of their son's age or older, even if the female is their son's teacher.
Is it a double standard? Yes.
Is it going away? No.