The man then approached the Education Council.
In submissions to the council's disciplinary tribunal, the teacher accepted she engaged in an unprofessional manner amounting to serious misconduct, the council decision said, and agreed to her teacher registration being cancelled. She had also resigned from her job.
A psychological assessment placed her at low risk of repeat behaviour, saying the incident "appears to have been a one-off occurrence".
"She does not display any concerning variables that are associated with sexual offenders," he said.
"Given her age, a history of [redacted] years of no further such behaviour, and the significant consequences for her since the allegations, it is his opinion that she can be considered as being at low risk of engaging in similar behaviour with any student again."
However, the council tribunal noted it was "concerned by what appears to be a lack of clear recognition or acceptance on the part of the respondent that she transgressed a fundamental professional boundary".
There was "little acknowledgement by her of that", it said.
"The tribunal wishes to state clearly that her crossing of that fundamental professional boundary with a current student was completely unacceptable whether assessed by today's standards or those of the '1970s'."
The woman was described as a fully certified teacher, who in recent years has held academic positions. It has previously been reported that she had been teaching at a school in Christchurch when the relationship occurred.