Tae Won Chung, 17, was sentenced in Auckland District Court to 18 months imprisonment after earlier admitting injuring Avondale College teacher Dave Warren with intent to cause grievous bodily harm.
Chung stabbed Mr Warren, who taught Japanese, in the back while he was writing on a whiteboard during a lesson on March 3.
The stabbing came after Chung was goaded about his fear of North Korea and returning home to military training, the court was told.
Mr Warren woke Chung as he dozed in his Japanese class on March 2, warning him "you'll be dead" if he slept while the North Korean army attacked.
Chung took a knife to school the next day, and stabbed Mr Warren in the back.
Mr Warren earlier spoke to him about South Korea's compulsory military training and how Chung would be conscripted into the army when he returned home.
His lawyer David Jones, QC, told the Auckland District Court the comments were "the catalyst for what happened the following day".
Chung was anxious about going into the army and the volatile situation there. The week before North Korea had been threatening to test fire missiles.
With a rising sense of anger, he went home, took a knife from the kitchen and put it in his school bag. The next day, as Mr Warren wrote on the whiteboard with his back to the class, Chung stood and stabbed him in the right side of his back, damaging his spinal cord and bending the knife.
Mr Jones said the comments were "culturally insensitive" but accepted Chung's reaction was unjustified.
"It triggered in him a response...this was not a random act of violence in the normal sense and culminated in the explosion of anger on March 3."
Prosecutor Deb Bell said Mr Warren wanted to stress that he was not racist. If Chung was upset he could have sought counselling or sought help but he "didn't do any of those things".
The Crown didn't accept the comments could be seen as provocation and sought a jail term of about six years.
Judge Roderick Joyce said Chung's attack had been "gravely reckless and could have proved lethal". He didn't accept there was a "powerful argument for provocation".
Psychiatric assessments revealed he had a problem with authority, low tolerance and poor impulse control. Judge Joyce said Chung had bottled up his difficulties with Mr Warren.
He said Mr Warren acknowledged friction between the pair existed but did not think it was greater than any other between a teacher and student.
Mr Warren told the court he would forever remember Chung "straddling" over him with a "bloody knife protruding and threatening me with the words `Don't ever **** with me'."
He was attending counselling, was fearful when strangers approached him from behind and was constantly checking that his doors were locked.
He was on light duties at work and could not do the things he used to enjoy because of ongoing leg problems. Doctors have told him they're not sure if he'll make a 100 percent recovery.
