The 31-year-old female teacher sustained minor injuries while Year 12 students Mikayla Eastwood and Hayden Perkins died at the scene.
The Eastern Fleurieu School community is mourning the loss, with principal Ian Kent advising parents of the tragic news on Wednesday morning.
“As a school community we are grieving the loss, and we know this event will affect our Year 12 group who are about the graduate,” he said in a statement.
The school is offering counselling to Year 12 students and Mr Kent said it would support the staff member involved during her recovery.
A Rite Journey Graduation planned for Wednesday night and school dance showcase organised for Thursday night have both been postponed out of respect to those involved in the tragedy.
The 17-year-old boy and his 18-year-old female passenger died after their Mazda crashed into a Hyundai i30 on Long Valley Road in Gemmells, about 50 kilometres from Adelaide’s CBD, at about 4.40pm on Tuesday.
The 31-year-old teacher was transported to Mount Barker Hospital for treatment.
The latest tragedy takes South Australia’s 2018 road toll to 68. It was 87 at the same time last year.
More on 7 News at 6pm.