The pair had been at a gathering at a friend's house when Elliott took the friend's car without asking and crashed it soon after about 1am on Heaphy Terrace.
The court heard Elliott had 110 demerit points on his driver's licence and faced suspension for being caught three times the previous year driving with passengers on a restricted licence and at speed.
Now 17, Elliott wept in the dock with his head bowed.
A packed public gallery listened as Shaun's family and friends described how his death had destroyed their lives.
Mr Nilson, a manager of two dairy farms at Te Kauwhata, said the pain, anguish, anger and loss of the love of his son was too much to bear.
"My son was not only my son, but a bloody good mate."
Mrs Nilson said she missed her cheeky, big-hearted boy, who was just five weeks from his 18th birthday.
"He was just finding out his true self and standing on his own, a fine young man that I was proud to call my son."
The couple had already suffered the loss of a 2 -year-old daughter, Hannah, 12 years earlier through drowning. Now their youngest and only surviving child, 5-year-old Laura, was also left devastated by the loss of her brother.
"I cry every day," Mrs Nilson said.
Grandfather Ray Humphreys said everywhere he looked he saw reminders of Shaun.
Though Shaun had consumed less than the adult legal limit of alcohol for driving, he was not wearing a seat belt and his parents said they could not understand why their "mature, well-rounded" son got in the car.
"For the people who think it's fair to put legal highs in all five corner dairies in the vicinity of Boys' High, I ask could this be Shaun's pitfall on the night of May 27?" Mrs Nilson asked.
She later said she believed her son must have also smoked a legal high to end up in the car with Elliott, who was only an acquaintance, because she and her husband had taught Shaun to be responsible with alcohol.
Justice Rebecca Ellis sentenced Elliott to three years without a minimum term and disqualified him from driving for four years from his release.
She took into account his guilty plea, age, remorse, good character and sporting achievements.