The Education Council is investigating allegations of a sexual relationship between a Christchurch teacher and a student more than 25 years ago.
Media reports say a woman, now 38, lodged a complaint with the council on Wednesday, alleging the male teacher had a sexual relationship with her when she was 12.
It has been reported she was shocked to learn he is still a registered teacher and still teaching.
In a statement the council's manager of teacher practice, Andrew Greig, confirmed it has recently received a complaint regarding historical allegations.
He said it had been referred to the council's complaints assessment committee for further investigation.