Ellowes Hall Sports College has sent a letter to parents saying the case of coronavirus was in Invictus Sixth Form Year 13.
The letter from Tuesday says: "We have been advised by Public Health England that there has been a confirmed case of Covid-19 within the Invictus Sixth Form in Year 13.
"We know that you may find this concerning, and as a trust, we are continuing to monitor the situation and are working closely with Public Health England.
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"However, I want to reassure you that due to the safe and secure manner in which we as a trust have worked and delivered lessons, both in Sixth Form and across all our schools, we have been able to isolate this one confirmed case to one small Year 13 class and identify all possible contacts.
"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 will be a mild illness.
"We have a small number of students in one class who we have identified as being in direct prolonged contact with the confirmed case yesterday and these students will have received an individual letter and will be staying at home for 14 days."