He said he only had one puff and was not intoxicated when he drove home.
"I couldn't really inhale it and I had to cough because it hurt. It wasn't for me."
The school's international director suspected one of the boys had been smoking marijuana and found out the story.
The student said he was called into a meeting with three senior staff members without a support person. He said he was told, "just tell the truth and nothing will happen".
But when he confessed, he and his family were given 24 hours to respond before his contract with the school was terminated.
Secondary Principals' Association president Tom Parsons said international students were held to a different set of standards to local pupils, which meant they were the school's responsibility around the clock.
"If he was a local student it would likely be out of the school's hands," he said.
"But he knew the consequences before taking that puff so welcome to the real world junior, you're now in a man's world."
The student's uncle, who is his designated caregiver in New Zealand, sought legal advice and a five-week stoush ensued.
He said the school was in part responsible for the incident because the boy who had sourced the marijuana had been placed in a home where he was exposed to the drug.
The uncle suspected that the was expelled because his parents had previously complained to the school about his care.
Further, the incident occurred outside of school and the boys were not in uniform so there was no damage to the school's reputation.
"He had a puff of marijuana because they all did it," he said. "No New Zealander would be expelled for that because it was outside of school - it's a police matter."
Immigration New Zealand has been notified and, unless he is accepted into another school soon, the student's visa will be revoked and he will have to leave the country.
Tauranga Boys College principal Robert Mangan said the school had zero tolerance for illegal drug use and the case was handled in-line with school policy.
"As per school protocols all parties involved were kept fully informed throughout the process and were given the opportunity to respond.
"Following this process the school management and its Board of Trustees imposed appropriate sanctions based on the degree of involvement of the boys who took part in the illegal activity."
According to Immigration New Zealand, there have been over 83,000 international secondary school students in New Zealand since 2009.
Education New Zealand foreign students contributed $2.6 billion to the economy in the 2012/13 financial year.
Aims Global Education & Immigration Services immigration adviser Amar Manchanda said such cases were noticed by the international student networks around the world, and could have a negative impact on the lucrative industry here.
"I think if they make one mistake they should be given another chance because they're coming from another country and they should be given the chance to prove themselves.
But if the school is adamant and they get sent home, then that person will be very negative about the New Zealand education system."
