A female teacher has resigned from her job at a Hamilton high school after allegedly performing oral sex on a senior student.

The teacher is reported to have performed the sex act on a Year 13 boy the night of the school leavers' dinner in November 2015, though not at the venue itself.

The boy involved complained to the school, but it was his word against the teacher's and no action was taken, a source who spoke on condition of anonymity said.

So the student swore an affidavit and presented it to the board of trustees.

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The incident was witnessed by other students and talk of it is "quite rife" among senior students at the school, according to the source.

"Everybody at the school knows."

At least one student at another school has said that the incident was talked about widely on Facebook last November.

The female teacher, who stuff.co.nz has decided not to name, is now under investigation by the Education Council.

The teacher went on sick leave and stayed on the payroll over the Christmas break before resigning in 2016, the source said.

The person did not know of any previous incidents of concern with that teacher.

The register of New Zealand Registered Teachers shows the woman, who is in her mid-30s, is fully registered but has "voluntarily agreed" not to teach while the investigation is running.

The principal and the chair of the school's board of trustees declined to comment on the matter - including the nature of the allegations and whether the teacher is still working at the school.

They said it would not be appropriate for the school to comment while the Education Council investigation is ongoing.

The Education Council confirmed an investigation is under way, but wouldn't comment on specifics.

"[The teacher] has undertaken not to teach while our Complaints Assessment Committee investigates certain allegations," Education Council spokesman Andrew Greig said.

"It would be improper and unfair to comment further because the investigation is active and we don't want to predetermine any outcomes."

Attempts to contact the teacher were unsuccessful.

A woman who answered the door at a house belonging to the teacher said she was not available, and a woman who answered the phone said "she won't be available" for comment.

Boards of trustees and principals are legally required to report issues they think could be serious misconduct to the council.

The council first looks at whether a complaint or report is valid, then gathers more information.

The next stage is an investigation and the teacher can be asked for a written commitment not to teach until it is complete.

After that, the case can go to the Disciplinary Tribunal, where the outcome could range from dismissing the complaint to cancelling the teacher's registration.

BAD TEACHERS

The Waikato has had several cases of sexual misconduct by teachers in recent years.

Former teacher Kelsey Rebekah Allen had a three-month sexual relationship with an 18-year-old student in 2014 while she was a physical education and health teacher at Morrinsville College. She lost her teaching registration.

Melanie Hendriks was stood down from her drama teacher position at St John's College in Hamilton in November 2014 after striking up a sexual relationship with two teenage students at the all-boys school. She lost her teaching registration.

Also in 2014, former South Waikato assistant principal Rueben James Parinui Tapara was sentenced to seven years in jail after pleading guilty to 10 charges of sexually abusing boys and one charge of selling/ supplying cannabis.

And in 2013 Turaki School teacher David Robert Ballantyne was charged with indecent assault of boys he met through church - he later pleaded guilty to one charge and was found guilty of another.

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