Pupils had been told the decision to make face coverings mandatory in schools would be reviewed after the first six weeks of term, but the First Minister told MSPs this would now be extended until the October break.
The Scottish Government will review the measure again then, the SNP leader said.
At Tuesday’s Covid-19 update to Holyrood, Ms Sturgeon said: “We indicated at the start of term that secondary schools pupils would need to wear face coverings in class for the first six weeks of term, subject to a review at that point.
“Given the high levels of infection still being experienced, the [education] advisory sub-group has advised that this requirement should remain in place until the October holidays, and be reviewed again then.
“I know how unpopular this is with many pupils and I understand why, but for now it remains a prudent and necessary precaution.”
Ms Sturgeon said updated guidance would also be provided to schools around which parents should be informed of positive Covid-19 cases in school.
She told MSPs that children who are low-risk contacts of positive Covid-19 tests will be told to take an additional lateral flow tests prior to returning to school to minimise the potential for further transmission.
Letters will also be sent to parents of classmates of positive Covid-19 cases.
The First Minister said: “These letters should be sent on a targeted basis to those who are most likely to have had low risk contact with someone who has tested positive.
"They ensure that parents, staff and pupils are aware of those cases – and they offer advice on issues such as looking out for symptoms, and using lateral flow testing.
“Our updated guidance may mean, for example, that it is appropriate to send letters to the classmates of a pupil who has tested positive, but not to everyone in their year group.
“We hope that better targeting will help reinforce the importance of the messages in these letters while minimising undue anxiety.
“All of these measures reflect our commitment to prioritising the wellbeing of children and young people – and our determination to minimise disruption to education."