Hundreds of teachers have criminal convictions and many are not fit to teach, newly released figures show.

Teachers have been investigated for sexual misconduct, violence, drug and alcohol abuse, incompetence, dishonesty and viewing pornography in the past two years.

The number of complaints has jumped by about half since the Teachers Council was set up in 2002 to vet teachers and independently investigate allegations of serious misconduct.

Of the 664 teachers whose behaviour triggered complaints since November 2009, nearly 300 were convicted of criminal offences.

Fourteen were struck off the Teachers Council register for serious code-of-conduct breaches or criminal offending. In total, nearly 50 teachers were stripped of their teaching licences in the past two years alone.

High-profile cases of misbehaving teachers include:

- A female teacher became pregnant with a 17-year-old high school pupil's child after they put the school yearbook together.

- A male teacher was caught with more than 200 pornographic images, including a videotape of his daughter and two foreign exchange students taking showers.

- Other cases include teachers viewing bestiality, committing theft, driving drunk and abusing illicit drugs.

Teachers' unions say their members are often targeted by aggrieved parents with spurious allegations. The complaint process could be personally "traumatic" and professionally damaging.

About 260 complaints, some vexatious, were dismissed in the past two years.

However, dozens of other teachers were formally censured for misconduct, referred for competency mentoring or referred to an impairment committee for medical or addiction reasons. Others agreed to voluntarily undergo monitoring because of concerns about their behaviour or teaching ability.

Figures released under the Official Information Act show 293 teachers were referred to the Teachers Council for criminal convictions. They included violence, sexual offending, drug and alcohol offences, pornography and dishonesty.

Teacher conduct sparked 277 complaints, including violence, dishonesty, sexual conduct, alcohol and drugs and pornography. Competency issues triggered a further 103 complaints.

Teachers Council director Peter Lind said every complaint was investigated initially by a complaints assessment committee. Most teachers met high standards and the number of complaints was small given the 100,000-strong teacher workforce.

The New Zealand Educational Institute (NZEI), which represents primary teachers, says schools sometimes make unpopular decisions regarding pupils, and teachers can be targeted unfairly by vexatious parental complaints.

"Sometimes the outcome for their children is not what they want from the school," NZEI national president Ian Leckie said. The union supported any initiative that vetted out serious criminals or inappropriate individuals from the profession.

Post Primary Teachers Association president Robin Duff said it was vital problems with errant teaches were investigated swiftly.

ROLL OF SHAME

A Northland teacher kissed a 15-year-old girl on a mattress, and his wife, the principal, failed to act, tearing up a written complaint. John Hone Riiwi Toia Mutu and his wife Deborah Anne Mutu were both deregistered for serious misconduct and ordered to pay $20,000 each in costs after a hearing in October.

Christchurch maths teacher Gerard Coulson resigned from Rangi Ruru Girls' School last February after being confronted about an affair with an 18-year-old pupil. A mobile phone photograph of the pair in bed was believed to have circulated at the school.

A married male teacher was deregistered in December 2010 after he "counselled" a pupil who had been in an incestuous relationship by having sex with her in his car and on a classroom floor during school time.

Two other married, male teachers were deregistered the same year. One had an intimate relationship with a year 8 girl he called his "first true love". The other had a sexual relationship with a depressed 16-year-old female pupil.