A South Waikato teacher has been stood down amidst allegations he had a sexual relationship with a student.

A high school teacher in Tokoroa is under investigation for allegedly sleeping with a 15-year-old student.

Details of the relationship were discovered by the girl's family and a complaint was made to police.

The male teacher, whom Stuff has chosen not to name, tried to kill himself.

"He was a popular staff member and even more so with the kids. He was what the kids would call skux [cool]," a former colleague who did not want to be named said.

On Sunday, once the relationship was exposed, the male teacher's plan to kill himself was foiled when a passer-by found him.

Police said they cannot comment on whether certain individuals are under investigation.

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However, a source said that police went to the school this week to inform the principal of the investigation.

The Ministry of Education also confirmed police are investigating the teacher.

A teacher in the town said it appeared the relationship had been going on for some time.

"I know there were messages containing photos that were found on her digital devices. They were having sex." he said.

"At this point the school board haven't told parents the details of why this teacher has been stood down."

"Behaviour like this is unacceptable. Not only do you tarnish your name, but you tarnish everyone associated with you. This girl is just that: a girl. We have a big mess to clean up now and some very hurt and vulnerable people."

The principal of the school said he could not answer any questions, but in a statement said: "The school is currently working through a matter and has consulted the Ministry of Education, New Zealand School Trustees' Association, Education Council and Police. We have no further comment to make while it is investigated."

Ministry of Education head of sector and enablement Katrina Casey said the ministry was notified of the police investigation by the school.

"The teacher has been stood down whilst this takes place," Casey said.

"We are working alongside the school to provide any support they need and to ensure that student safety is not at risk.

"Our traumatic incident team have visited the school to assist staff and the principal to ensure the day-to-day running of the school is not affected."

The Education Council, formerly known as the Teacher's Council, released a statement saying: "We are expecting to receive a mandatory report concerning [name withdrawn] today. Once that is received, we will be able to assess if an investigation is required. We are satisfied there are no issues regarding the safety of students."

A friend of the girl's family said family members are supporting the girl through this.

"The whanau are strong. As soon as they knew, they flew into action to make sure [she] was well supported. The gossip is rife among the high school kids at the moment - and it's just going to get worse once police lay charges."

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