The entire Year 7 cohort at another Bristol school is now confined to their homes after a pupil tested positive for coronavirus.
Oasis Academy Brightstowe in Shirehampton has told parents not to be "alarmed" after a Year 7 pupil was confirmed as having COVID-19.
All pupils in the same year group have been instructed to self-isolate until Monday, October 5, in case they have been infected.
A letter sent to parents on Monday (September 21) read: "We have put extensive measures in place to ensure that our students and staff are as safe as possible as we have welcomed our young people back to school.
"This is an isolated individual case in the Year 7 bubble, so please do not be alarmed, but it is a reminder that we all need to remain vigilant, both in school and in the wider community.
"We are continuing to monitor the situation, working closely with Public Health England.
"We know that for most people, coronavirus (COVID-19) will be a mild illness, but we all have a responsibility to ensure that we do all that we can to reduce transmission to others."
The school remains open to students in Years 8, 9, 10 and 11, even if they have a sibling in Year 7, as long as they are not showing any symptoms.
A separate letter sent to parents of children in Year 7 advised that they could have been in close contact with the affected child, and so should stay home as a precaution.
The letter advised: "We are asking you to do this to reduce the further spread of COVID-19 to others in the community.
"If your child is well at the end of the 14 day period of self-isolation, then they can return to usual activities."
It is the second Bristol school in the Oasis Community Learning trust to confirm a case of the virus.
Oasis Academy John Williams in Hengrove sent Year 7 home at the start of term after a pupil tested positive.
Bristol Live now knows of confirmed cases at about a dozen schools in the city, and more in the neighbouring districts.
Oasis Brightstowe is not the first school in the neighbourhood to be affected - Shirehampton Primary School also confirmed a case among Year 6 at the start of term.
