The girls were part of a group of 102 Columba College pupils, including 84 Year 9 and 18 Year 13 pupils and seven staff on a school outing.
As the Otago Regional Rescue Helicopter departed with the injured girls, teacher Joanne Weggery thanked the three surfers, Tom Leckie, 24, Dillon Ryan, 33, both of Dunedin, and Tony Denley, 32, of Osborne.
"Everything is for a reason. Bless you. Thank you so much."
Mr Leckie said that before lunch, the three men debated which of the many breaks they could surf in the area and decided on the remote Canoe Beach.
When they arrived there were pupils "swimming in the shallows" and the surfing was good, but after catching their fifth wave they heard yelling.
About 100m from shore, there were 30 pupils out in deep water, sucked out by a "severe" rip, Mr Leckie said.
The students were yelling, panicking and waving their arms and were being held in the rip.
"They were going around and around and around and around."
The men paddled out and rescued four girls at a time, pulling them from the deep water and taking them to a large inflated tyre tube that was floating further inshore.
The men made four trips to the girls and each time the tube was full, two swam it to shore as the exhausted girls hung on.
About six students caught in the rip were strong swimmers and helped the others until the men returned, Mr Leckie said. The beach was deceptive because it had a gradual incline and then rapidly dropped off to deep water.
"They were lucky. Without help, there would have been a few fatalities."
"Definitely," Mr Denley said.
As the men left the beach to return to work, many pupils returned to the three buses that brought them to the beach for the day of bonding.
Many students were covered in blankets, some holding tightly on to the handrail and struggling to walk.
One said the day was supposed to be a way to get to know everyone and in a way it had brought them together.
She would always remember a student vomiting blood on the beach and the bravery of the surfers, she said.
"Thank you. You saved so many girls' lives. We will be eternally grateful."