What you guys are missing is that the teacher is in a position of power (male or female). They are taking advantage of a trusted position and using it to exert even more power. Rarely are these relationships about love or sex but about one party exerting influence over the other. So we can joke and say the kids aren't victims but in all likelihood they will have trust issues and problems with authority further down the road.
While that is certainly possible, and why it makes sense to fire the teacher, that seems like a massive blanket statement to say that they all are just using their power to get sex.