St Kevin's College principal Paul Olsen said the school was dedicated to helping Watson's family during the challenging time.
"We are hoping that the love of the local community for Watson will be expressed by wanting to help the family at this awful time. The fact he also has a father in Fiji, and family all across the world, has also meant everything has been more complicated and costly for the whanau," Olsen said.
The school had also been supporting Watson's family in Fiji and the local Fijian community.
"We have been very conscious of the incredible pain his father in Fiji must be feeling, and with Covid-19 restrictions, how tough it must be to have been so far away from him. We deeply appreciate the support that has been given to us from our local Fijian community in the wider extended community."
Watson started studying at St Kevin's two years ago on an educational scholarship, and quickly immersed himself in school and sporting opportunities, and was a school prefect for Whyte House this year.
Olsen described Watson as the "best of the best", who was a big man on the rugby field, but even bigger off it.
"He had a heart of gold and was an amazing role model. He was a great athlete, but took time to encourage even the smallest and least able kids to do their best.
The school's counsellors, deans and hostel staff were offering support to pupils.
A funeral would be held at St Kevin's College chapel at 1pm on Saturday. The family welcomed anyone wanting to attend, Olsen said.
Senior Sergeant Jason McCoy, of Oamaru, said police passed on their condolences to the family and the wider community.
The crash was still under investigation.
Anyone wanting to donate to support Watson's family can do so here.
