The fact is utilizing those you have power over for pleasure is always questionable- regardless of age...
I guess we could debate the 'age of consent' issue, but no conclusion we can come to will be meaningful- I have known teens that were far more sexual than most adults (and let me be clear I did not know them in ANY carnal way), and I have known adults that were obviously way to immature to be engaging in sex...

When I taught classes it was made clear that fraternization with the students would end your future (ie you would be kicked out of grad school)- I once VERY accidentally brushed my arm against a VERY attractive student's ummm behind... she had stepped back as I was walking by- I spent many hours worrying about an accusation of sexual impropriety, but she understood it was an accident and apparently didnt think anything of it... but if she had felt it was intentional and brought charges I could be homeless now... We need to find a happy medium with our rules...Professors having affairs with students is not that rare, and when both are adults I have no problem as long as the student isnt in the teacher's classes....

When the affair is with someone under 18, I have to say the offender is at the VERY least guilty of stupidity... and USUALLY guilty of abuse- this teacher may have made this guy's fantasy come true- but she needs serious treatment... if the kid was ok with it why did it become a legal issue? I assume it is because it did trouble him....

And now for the gender issues raised by this- it is true that a man that did this with a girl would be IMMEDIATELY arrested and labled a pervert for the rest of his life... When women do this, and lets face facts women rarely do this compared to men, they do NOT get the same jail time....

I think the woman in question needs jail and treatment- but not a life long term....

The funny thing (and not making light of the situation) is this kid is going to be a hero to his classmates...