Her mother withdrew her from the classes and reported the indecent assaults to police.
A second victim was also indecently assaulted on several occasions before she broke down crying and disclosed to her mother what was occurring to her and her friend, also a victim, before the police were notified.
Two other victims spoke about Harter's behaviour amongst themselves and wrote a letter to their teacher asking him to stop making them feel uncomfortable before also informing the school's principal.
The remaining victims were abused in similar circumstances at Harter's home and at the school. Harter had stated he believed one of his victims was encouraging the behaviour and was happy with it.
He admitted the entirety of the offending to police and said he became sexually aroused when he touched his students.
Judge Bridget Mackintosh remanded Harter in custody until his sentencing on October 23.
She said Harter had abused his "position of trust" and believed Harter would be given a prison sentence, given the nature and scale of the offending.
Harter faces a maximum prison sentence of 10 years.
Harter was initially granted interim name suppression. However, his name was revealed after an application by the school's board stressed the need for his name to be made public.
Hawkes Bay police released a statement this afternoon, following Harter's guilty pleas, urging any more victims to come forward.
Detective Sergeant Nic Clere said the police investigation was continuing as it was possible there were more victims who had not yet come forward.
Police had met the school's board of trustees and pupils' parents to inform them of the investigation process.
An 0800 number and email contact for parents of children who were taught by Harter had also been set up, Mr Clere said.
"The investigation team has established that Mr Harter has taught many children during his 40-year teaching career in Hawkes Bay, Wellington and Masterton."
Parents could contact police by calling 0800 DAYTON -- 0800 329 866 -- or emailing Operation.Daytona@police.govt.nz.