Robert Selwyn Burrett has admitted sexually abusing 12 girls while working as a school caretaker and bus driver in Christchurch.

A school caretaker and part-time teacher who sexually violated girls in his underground shed has been struck off the teachers' register.

Twelve Christchurch primary school girls, three of them disabled, were repeatedly raped, sexually violated, indecently assaulted, or made to watch pornography in the caretaker's shed or on a school bus.

In "a horrific abuse of trust", described as one of New Zealand's worst cases, Robert Selwyn Burrett, 64, a school caretaker, bus driver and part-time teacher, installed curtains and a lock in his school caretaker's shed to sexually abuse them.

One girl aged 10 to 12 – the victim of repeated rapes – said it happened "most days, at morning tea and lunch time during school". The victims ranged in age from five to 12 years.

The school where Burrett worked as a caretaker has defended its procedures. It believes it could not have done anything differently to discover his offending earlier.

Burrett worked as a bus driver for disabled children at another school. The bus company was contracted to the Ministry of Education, which police-checked him before he got the job.

The Education Council had Burrett struck off on Friday afternoon. He had been a registered teacher since 1991.

Education Council manager teacher practice, Andrew Greig, said this sent a message to the friends and family of the young girls involved that he will not teach again.

"This is the final step in the process. Our role is to ensure teachers are of a high standard and safe to teach. We take that role very seriously. The public would expect this."

Burrett was not a practising teacher when the offences came to light, but was still on the teachers register.

SCHOOL DEFENDS PROCEDURES

The board chairman at the school where Burrett was a caretaker said the school did as much as it could in vetting Burrett before hiring him.

The school felt it could not have done anything differently to discover his offending earlier.

It had since made "minor changes" to supervision procedures during intervals and lunchbreaks.

Burrett was a relief teacher before he became a caretaker at the school. His bus driving role was for a different school, the chairman said.

With the introduction of the Vulnerable Children Act in 2014, after Burrett was hired, it gave more scope to vet school staff - "which is good", the chairman said.

The school would keep its "close-knit" community aware of what was going on as much as it could, the spokesperson said.

"The school has continued to work hard to support the families involved and the wider school community."

The underground shed where Burrett's offences took place still existed, but the new caretaker used it less.

Instead of storing tools there, the new caretaker brought them to school each day.

ABUSE CONTINUED FOR YEARS

The Christchurch High Court was told on Friday that the abuse of girls as young as five, including some with physical and mental disabilities, had continued for years.

Children saw him abusing other children. One of the girls involved was strapped into a specialised chair and could only communicate through an electronic device.

The abuse, involving 12 girls ranging in age from five to 12 years, included rape, sodomy, forced oral sex, indecent assaults, video-taping of the offending, and watching pornography.

The court heard Burrett was employed as a school caretaker from early 2013. From 2013 until last year he was also employed as a bus driver transporting special needs pupils from their homes to primary school each day.

All of the pupils on his bus run suffered some form of disability that made communication difficult, or impaired their physical or mental functioning.

Burrett repeatedly invited one girl aged between eight and 10 into his underground shed on the school grounds where he would talk to her about "adult stuff" and told her not to tell anybody.

When she walked up the steps from his shed, he would touch her bottom.

When he met her as she walked to school one day, Burrett hugged her, kissed her on the cheek, and told her to be good in class. The girl thought it was "weird and gross".

Many times, Burrett took two girls, aged nine and 10, into the shed where he committed indecencies, and raped one of the girls.

He showed two girls pornographic videos during the school intervals. Objectionable images and animations involving children were found on his computer.

He indecently touched one girl after asking her to help him pick up rubbish.

After sexually violating a girl aged five to seven, he told her not to tell anyone or he would "smash her", prosecutor Deirdre Elsmore said.

She detailed other offences including sexual violation by unlawful sexual connection and indecent assault which Burrett had committed while bus driving.

He told one girl "about sexual matters, and what sexual things he did with his wife".

When spoken to, Burrett admitted some hugging and touching involving three girls, but then said nothing more.

Burrett had been in custody since his arrest last year, when his name was published but a suppression order covered details of the charges except for the fact they related to sexual offending.

Those details could be published after Burrett's guilty pleas on 21 charges in the High Court at Christchurch before Justice Cameron Mander on Friday.

The judge continued suppression orders on the name of the school and the bus company, but the issue would considered again at Burrett's sentencing on April 12.

BUS COMPANY CONTRACTED TO MINISTRY

Burrett was a qualified Special Education School Transport Assistance vehicle driver. He worked for a company contracted to the Ministry of Education.

Ministry of Education Deputy secretary Katrina Casey said Burrett underwent a mandatory police clearance check to become qualified.

The ministry checked all records for any historic complaints received during his employment, but none were found.

"The serious criminal offending Robert Burrett has admitted today is appalling and should be condemned. Our sympathy goes out to his victims and their families."

The ministry was supporting the schools, families and communities involved and worked with police and Child, Youth and Family in their investigations.

'HORRIFIC ABUSE OF TRUST'

Sensible Sentencing Trust spokesman Garth McVicar said it was among the worst cases he had come across.

"It's one of the most despicable cases I'm aware of," McVicar, who planned to travel to Christchurch for Burrett's April sentencing.

"It's a horrific abuse of trust, involving disabled children.

"I'm actually lost for words and I deal with a lot of this type of stuff."

He said people were right to wonder how Burrett could offend for more than two years, but sex offenders were "very manipulative".

"They're very cunning, and the ages of the children he's preying on, the fact he talked about the type of stuff he did with his wife, he tried to normalise it.

"Then he used threats of violence against children who told on him. Between the powers of manipulation and threats of violence . . . he was able to continue the offending for as long as he did."

Burrett's only previous run-ins with the law were two driving offences in 2001 and 2007.

BURRETT MAY BE STRUCK OFF

The Education Council had Burrett struck off on Friday afternoon, since he was still listed as being registered to teach. He had been a registered teacher since 1991.

Police made the Education Council aware of the sex charges facing Burrett on May 12, 2015, a council spokeswoman said.

The council then enforced a voluntarily order where Burrett agreed not to teach while his conduct was investigated.

Burrett's last teaching job ended at the end of 2012. His latest practicing certificate expired on March 15, 2013.

The Education Council was aware of Burrett's two previous driving convictions.

In order to gain a practicing certificate, there was a "robust" procedure where teachers were vetted by police every three years, the spokeswoman said.

"We don't see that there were any problems with the way things were done."

Changes to the Vulnerable Children Act meant state-funded services and their contracted providers were now required to vet and screen the children's workforce and have child protection policies. Also, those who worked with children would need to have their checks updated every three years while their employment or engagement continued.