The police summary of facts said a telephone conversation between the victim and Robb was recorded and used as evidence.
Crown prosecutor, Michele Wilkinson-Smith, said this year when the trial began the victim gave evidence twice and was cross-examined twice.
"The Crown does not accept remorse. He did not plead guilty until he had no option."
Wilkinson-Smith said Robb and the victim became close and exchanged cell phone numbers on a sports tournament in Christchurch.
"The defendant travelled from Levin to Whanganui to meet up with the victim after school.
He drove her to Kai Iwi Beach and performed oral sex.
"On a second occasion the defendant picked up the victim and drove her to a motel where they had sex," Wilkinson-Smith said.
Three victim impact statements were heard in court: an audio recording from the victim, a letter from the victim's mother and a letter from the victim's stepfather.
"You told me what you were doing was okay and it felt good. I had a naive belief of a child thinking I knew best but you affected my personal state of mind," the victim's impact statement said.
The mother of the victim said she was broken-hearted with the breach of trust.
"You gained our trust as her coach and brainwashed her with text messages," the victim's mother said.
"Kevin Robb, you robbed my daughter of the joy of life and freedom that a teenager should have and when she told me I could never tell anyone I knew she had been groomed by an expert.
"I feel anger to the point of rage," the mother said.
Robb's defence lawyer, Peter Brosnahan, said it was easy to be critical of Robb's delayed guilty plea but human nature played a part and that needed to be recognised.
"In the telephone conversation he acknowledged his actions and after he had to deal with the impact it would have on his family," Brosnahan said.
Brosnahan said Robb had written a heartfelt letter of apology and he must be given the maximum credit for his good character.
Judge Philip Crayton said a clear message needed to be sent to protect young vulnerable people.
"The age of the victim reflects moderate vulnerability but the age difference is of top level. You were 44 years old and she was 13 years old.
"You breached trust as a sports coach to her and her parents. There was a high degree of pre-meditation and grooming that lead to repeated incidents of sexual conduct," Judge Crayton said.
Judge Crayton ordered Robb to pay $10,000 for emotional harm and reparation to the complaint's family and sentenced him to two years and six months in prison.
