The students in Year 11 at Oldbury Wells School, Bridgnorth, have been told to remain at home in a letter sent to parents.
At Welshpool High School years 10 and 11 are affected.
I have been notified of another positive case of Covid-19 over the weekend. This means that all pupils in Year 10 and Year 11 must not attend school until further notice.— WelshpoolHighSchool (@WpoolHS) November 22, 2020
The beginning of November saw pupils in Year 10 at Oldbury Wells self isolating.
They went back to school on November 6.
In the letter to parents the school said it was continuing to work with Public Health England and monitoring the situation.
It said Year 11 pupils should self isolate and stay at home until December 3.
Other year groups should be in school as normal.
The school has reassured parents that there are no worries over links with school transport as the confirmed case did not use school transport.
Across the Welsh border, Welshpool High School has also revealed that both its Year 10 and Year 11 pupils are being asked to self isolate.
In an announcement on Twitter today the school said all pupils in the two years must self isolate until further notice.
"I realise that this is frustrating, especially for the parents of Year 10 who have had three letters in relative quick succession," it said.
"However, this decision is based on a different positive case that affects both year groups."