Glossopdale School has asked pupils and staff to wear face coverings again from Monday (12 July) following a "significant increase" in the number of Covid-19 cases in school.
Pupils and staff will be expected to wear a plain blue or black covering in classrooms, when transitioning between lessons and in the Heart when not eating or drinking.
In a letter to parents, head teacher Debbie McGloin said the school community has "begun to be adversely affected" by both staff and a "high number" of students self-isolating due to positive cases of the virus.
"We have robust systems in school and a risk assessment is securely in place to minimise transmission," Mrs McGloin explained.
"However, it is clear that the lifting of restrictions has led to a rise in the infection rate locally and that, in school, we need to take action to keep the community safe."
From 17 May, in line with Step three of the government's roadmap, face coverings were no longer recommended for pupils and students in classrooms or communal areas, in all schools and Further Education providers.
Meanwhile, the Hadfield-based secondary school has also reminded parents to make sure their child takes a Covid-19 test twice a week, on Monday and Thursday mornings, and email positive test results to firstname.lastname@example.org.
"We have been providing LFD test kits for students since March and I would like to thank students and parents for continuing to test and provide us with the results," Mrs McGloin said.
"Although I know many find this difficult, and frustrating if their child is identified as a close contact, this is a vital part of our community effort to reduce transmission of Covid and therefore to stop it spreading into homes and risking vulnerable family members."
The headteacher is particularly urging Year 10 pupils to take a Covid-19 test on Sunday evening or Monday morning before returning to school following work experience, with there being a high potential for transmission of Covid-19 after mixing within and beyond the local community.
With lockdown restrictions due to be lifted on 19 July, before the school breaks up for the summer holidays on 22 July, Mrs McGloin has also asked for parents and students to "use those freedoms with due care and consideration for all around them".