I'm of the viewpoint that the adult should know better.
The teacher's purpose.. is to be present to educate young minds, and to show them "The right path", so to speak.
While the teenager might know "it's wrong", he's also at the age where his hormonal desires and fantasies might and will outweigh his rational judgement.
The teacher is supposed to know. ""Okay, I;m here to teach this young mind, to be honest, and do good".
If the teacher knows "It's wrong, and according to school policy, illegal, to.. cheat on an exam"..and there are consequences for such, academically, suspension, etc. How could they not know it's wrong, and there are, should be, consequences, for having sex with a minor?
Case in point.
I attempted to cheat on an exam, exactly one time in my entire school career from kindergarten, all the way through college.
I was having trouble in this class in freshman year of High School, and attempted to put a sheet with copied answers, in a place inside/underneath the desk where I thought the teacher couldnt see the exam.
Well, I was wrong. The teacher did see the exam, and immediately sent me to the Dean's office.
The Dean didnt even yell at me. He looked at me with a very calm, disappointed tone.
He said. "Mitch, you should know better. You know you're not supposed to cheat on exams, and if you dont know the answers honestly, you need to accept whatever grade you can earn honestly".
"As disappointed as I am to do this, I'm going to have to suspend you. I cant allow your attempting to cheat on an exam to go without consequences".
Not only did he suspend me, but, his punishment was even more severe. He suspended me for the rest of the school year, and I had to take the rest of my exams, at home, with a tutor that I had to pay for.
After that, I got the message, and never, ever, even attempted to cheat on an exam again.
That's what I mean, in another way, about students sometimes making poor decisions, and the teachers/authority figures, needing to show them the way. "