There are a lot of reasons because of which a student-teacher relationship is prohibited almost everywhere in the world. Discrimination between the students and distress among the student-teacher involved are just two good enough reasons behind it.
Such a thing recently happened and strengthened the cause when a Texas teacher went into a sexual relationship with two of her students.
She was arrested after the authorities were informed of her alleged 'hook up' with a student.
When she went on a ministry trip with one of her student, 17 and his family. She is known to have intimate encounters with him more than 10 times. Their relation ended with a little more drama.
Which happened on an invite from her to another student, again 17 for a hiking trip at Commons Ford Park, which lasted few hours, as told by the other student. She also later asked him to delete their conversations as she tried to hide it from her side too.
As the second student started bragging about it everywhere and led to her arrest. Although both the students were of legal age of consent, the inappropriation of the relations was illegal and thus she was arrested and charged.