Reuben Tapara, 33, pleaded guilty in the Hamilton District Court on Wednesday to 10 sex charges and one charge of supplying cannabis to a young person.
The boys, who were aged between 11 and 12 at the time, were students at the school
The most serious charges of sexual violation relate to a boy who was 12 when the offending began and which lasted nearly three years.
The court was told Tapara violated him on a number of occasions, offering him money in return.
The boy's mother read an impact statement to the court, in which she said Tapara had killed her son's childhood and innocence.
Judge Thomas described the offending as a gross abuse of trust, which was cynically planned and was premeditated.
But he said he believed Tapara was genuinely remorseful and gave him credit for this and his early guilty plea.
The court was told that it was only through information Tapara gave police that the two other victims were identified.
Judge Thomas described the offending against those boys, both aged 11, as less serious but also a breach of trust.