"Susie was a much-loved volunteer helper at the campus over many the years.
"Sadie was in Year 12 at Kaipara; Jamie, was in Year 13."
Mr Watt said three other young people from the Kaipara campus were injured in the accident.
"The loss is a tragedy for the family and the wider community and will impact the school in the days ahead.
"Staff and students at Kaipara are being provided counselling during this very difficult time.
"Our thoughts and prayers are with the families involved," Mr Watt said.
Mrs Stewart was the front seat passenger of the vehicle, Sadie was the rear left seat passenger and Jamie was in the middle rear seat.
Northland Road Policing Manager Wayne Ewers said the vehicle, which the three were travelling in, was driving east left the road on a right hand bend before it hit a large tree.
The ute was carrying seven people.
Its driver and rear seat right side female passenger received minor injuries, while the two males on the tray were thrown from the vehicle at point of impact with the tree, landing a short distance away.
Both males were taken to Whangarei Hospital with non-life threatening injuries.
The Serious Crash Unit is investigating the crash and will look into what charges, if any, may be laid against the driver.
