I don't think that the law can have it both ways. If it isn't against the law for a person - of any age - to have consensual sex with a 16 year old - then teachers shouldn't be treated as a prosecutable, special case. If 16 is the age of consent - then that should be that; of course, whether or not a teacher's position in a school would be tenable if such a relationship were to become common knowledge is another thing.