He bathed with the boy, took photographs of him naked and performed sex acts while the boy was in his care over four days at a sports tournament in Dunedin and while the boy's parents were on holiday in Nelson.
In another incident, Keys visited the family home and trapped the boy in his room by sliding a set of drawers in front of the door. He then drew the curtains and assaulted the boy.
When questioned by police, Keys said he had been confused sexually at the time.
Keys was one of the longest-serving teachers at Hutt International Boys School, having taught at the Upper Hutt integrated school for 19 years since it was founded in 1991.
He was charged earlier this year and resigned from the school at the end of last term.
The school's principal Grahame Duffy said the charges were disappointing but he stressed that they were historic.
He said the school would now try to move on.
