Two front teeth were also broken.
Warren told police he punched Mr Taui in the face once as he was angry at the victim for wearing Ngongotaha-labelled clothing.
Mr Taui's mother, Melanie Eagar, said her son did not want to take part in the restorative justice scheme as he did not want to be in the same room as Warren. Miss Eagar told the court that after the incident her son was with her in a shop when they saw Warren and her son started shaking and sweating.
Miss Eagar said her son had to perform in the back row of a kapa haka competition as his teeth kept falling out.
"He [Mr Taui] is a changed boy. He is quite an angry boy."
Warren's lawyer, Wiremu Te Are, said the consequences were enormous and Warren was remorseful. He was supported in court by his parents Aaron and Tanya Warren who were shocked by what he had done.
Mr Te Are said there was some history behind the incident but Warren had gone off "half cocked". Warren's employers and parents, who part own Rotovegas Boxing Gym, had to stand him down as they thought it was inappropriate for him to continue coaching young students.
Judge McGuire said Warren was a very good boxer and had been doing good work in leading other students. Warren had been a coach and mentor for children.
"You have been involved in a leadership training programme for students but what you did on that night was not what a leader would do. It's what a bully would do," Judge McGuire said.
If there was one lesson that Warren had to learn it was that because of his ability at self defence and boxing, others were going to "sucker punch" him to get involved in incidents as they were "too gutless".
"This is a massive setback in your life and it ruins the good things that you have done . . . You have let yourself down very badly. It will be a long journey back."
Judge McGuire said the victim faced a long road ahead and needed ongoing remedial dental work. The victim's family would be out of pocket by an estimated $9000.
Outside court Miss Eagar praised the judge's sentence. Both she and Mr Taui's father, David Taui, hoped Warren had got the message.
She said the dental work her son would need would cost about $25,000 and ACC was not covering all of the costs. Mr Taui was to have teeth implants when he turned 21.
David Taui said he did not want Warren to go to jail.
"Let's hope that he never does that again. The only thing we are grateful for is that our son woke up."
Having lived with a plate and two false teeth since he was a child, David Taui said he did not want his son to have to wear a plate for the rest of his life.