Gross. It's statutory rape no matter what the genders.. He's too young (in the US mind you) to consent and she's in a position of authority over him. This is why it's against school policy to fraternize with students, in college as well. It's the same in the workplace, most companies have a similar policy with bosses/workers because positions of authority can influence and take advantage of the person under them.
I personally find it *really fucking stupid* that guys are like "lol where was she when i was 16 lol" so you want to have been raped and had your teacher fired from school and prosecuted and shunned by her peers just to have sex with her?? Not to mention how it messes with some of these boys psyche and they need therapy for their trust issues and sexual confusion. Lol yea sounds fun guys