Blue Coat Church of England Academy sent a letter to parents on September 18 about the case.
The letter says: "We have been advised today Friday 18th September that there has been a confirmed case of Covid-19 within the Year 9 bubble.
"Upon investigation and undertaking an assessment of risk with Walsall Public Health, we have been able to narrow down any prolonged close contact to certain classes.
More Covid-19 coverage:
"We are continuing to monitor the situation and are working closely with Walsall Public Health.
"This letter is to inform you of the current situation and provide advice on how to support your child.
"Please be reassured that for most people, coronavirus (Covid-19) will be a mild illness.
"The school remains open for all staff and students, with the exception of those who we have contacted directly.
"We are following strict hygiene measures, providing your child remains well they can continue to attend school as normal. We will keep this under review."