Yes, but only in a positive direction. I would argue that the teacher acquires a newfound interest in the sexual student while maintaining the same interest in all other students. In essence, the level of care in the classroom, if measured quantitatively, can only rise.
Your romantic and outdated view of the student-teacher relationship has no place in this scary time and place, comrade Iron! Teachers do act with self-interest, and it is absurd to suggest otherwise. Allowing sexual relationships simply allows a little more joy in the classroom, and with the proper checks and balances, the favour bias could be regulated by an outside source without detriment to the hawt relationship forged by the consenting, of age student and their busty, horny and taut-skinned teacher.
I do concede that their could be a risk of the teacher having a far too powerful position in any relationship, but I also suggest that most teenager's have enough guts and determination to stick it to their teachers in most cases, so this would no longer be an issue. Once again, with an external balance there would be no need to submit for grades, as exists in American university culture.
It would also decrease tension in the classroom, leading to increased concentration and elevated grades! This is self evident stfu.
This makes the consent issue re the 16y/o negligible imo. Far better policy to impose a blanket ban on all such relationships, even if we do agree that a particularly strong-willed student (rare) could theoretically achieve an appropriate power balance in the relationship