If he's 16, she should go to jail.
My father's parents got married when he was 28 and she was 16 and a high school graduate. To treat 16 and 17-year-olds as "children" for statutory rape purposes makes no sense to me.
Of course there is a double standard regarding teenage boys versus teeneage girls, and there will be until teenage boys can get pregnant. I also believe that a relationship with any adult would be far more emotionally danaging for a teenage girl than a teenage boy.
Sexual relations between teachers and students are inapropriate; any teacher who does this should be fired and suspended from teaching for a number of years. I don't think these relationships are necessarily criminal; that depends on the law, which as I said should set the age at 16 not 18.