Ashburton College opened its doors on Wednesday to just 11 of its 550 Year 9 and 10 students.
The students will work in two school bubbles during Level 3 restrictions.
Principal Ross Preece said parents had heeded the message that only those who absolutely needed to attend school should do so.
Students were at school because of their parents’ work, or if they did not have access to online learning.
School staff had completed a property inspection, done necessary maintenance and had cleaned prior to the reopening.
He, his senior management team and some middle management staff would be at school to help supervise pupils, but no regular teaching staff would be present.
Teachers would continue to teach at home through distance learning.
Mr Preece said the school had its role to play in supporting the country get back on its feet and the economy moving.
He said there had been challenges over the last few days, but the college was open to support school families.
The work students were doing at school was no different from their peers working from home.
Face to face classes operated with appropriate social distancing measures.
Mr Preece said a system had been established to record onsite attendance and a contact tracing register had also been set up.
There was no canteen, no drinking fountains and all students were bringing their own lunch and drink.
Where possible, students also brought their own devices for the six hour school day.
Mr Preece said hand sanitiser was provided at the entry to classrooms and in bathrooms, and break times were staggered.
To support contact tracing, students were required to sit in the same place each day.
Registers identified which children were in each teaching space and recorded when and who they had contact with during the day.
Mid Canterbury schools have seen just a trickle of students return to the classroom under the new Level 3 restrictions.
Hampstead School had 13 students back onsite on Wednesday and there were 20 at Ashburton Intermediate, 10 at Netherby, 6 at Rakaia, zero at Longbeach, 25 at Borough School, 9 at Mount Hutt College, 20 at Allenton School and 13 at Ashburton Christian School.