WELLINGTON, Dec 10 - Samuel Jacob Zarifeh, 27, was on a private rafting trip with a group of teachers from the schoolwhen the raft overturned on the Landsborough River, inland from Haast.
There were four people on the raft when it capsized about 6pm on Saturday.
Mr Zarifeh's body was recovered by police, 45km downstream.
Headmaster Nic Hill said Mr Zarifeh was a physical education teacher and a house master at the school's Adams House boarding facility.
"Sam is loved by the Boys' High and Adam's House communities.
"Our heart's go out to Sam's family, his friends and the wider Christchurch Boys' High Community."
The school was supporting those affected, including getting those who were there at the time of the accident back to their families safely.
"Sam's death will be difficult for us all. I know that we will support each other," Mr Hill said.
Tributes to Mr Zarifeh are being posted on the school's Facebook page.