Outside of mental issues, a 14 year old knows damn well what they are doing
Then again, young minds are easy to manipulate. Maybe this 14 year old will grow to feel a betrayal of trust between teacher/student and grow to be unable to develop relationships w/ other adults/women because of this.
Or, maybe this 14 year old will figure he can scope every woman in sight and grow to be a habitual sexual harrasser who cannot keep a job as a result.
Or, maybe he thinks he is in love with the teacher and will become despondent over the "breakup" and he will become depressed and his grades will suffer.... maybe he drops out.
My point is,
1:
14 year olds are easy to dupe/manipulate, ergo they don't always "know damn well what they are doing"
2:
This scenario may very well have long term, negative effects on the victim.