A number of pupils at Richmond School have been told to self-isolate following a confirmed case.
Parents whose children have been in close contact with the school member have been told their child must isolate for 14 days.
Parents were contacted by phone and email this week.
It is understood the confirmed case was within year 10.
The confirmed case at the school comes as the latest official data shows there were confirmed cases in Richmondshire last week, including ten on Tuesday alone.
Localised figures show there were 13 cases in Catterick Garrison and Colburn between September 16 and 22, and five in Richmond over the same period.
The email to families affected stated: “We have been advised by Public Health England that there has been a confirmed case of Covid-19 within the school.
“We have followed the national guidance and have identified that your child has been in close contact with the affected child.
“In line with the national guidance we request that your child now stays at home and self-isolate until the end of Wednesday, October 7, returning to school on Thursday, October 8, 2020.
“We are asking you to do this to reduce the further spread of Covid-19 to others in the community.”
The letters stats that other members of the household can continue normal activities provided their child does not develop any symptoms within the 14-day isolation period.
Jenna Potter, headteacher at Richmond School, said: “On Saturday 26th September, we were made aware of the first confirmed case of Covid-19 in our school.
“Through our tracing system, we have been able to check and identify the Year 10 students who have been in close contact and have spoken to their families to advise that they now need to self isolate for 14 days from their last contact with the student.
“The response from parents has been entirely supportive and helpful.
“We have also written to parents of all students at school, informing them that we have had a single, positive case and reminding them of the guidance to adhere to.
We continue to follow DfE guidelines at all times and are working closely with Public Health England.
“Students remain in Year group bubbles and the school maintains seating plans for all lessons and lunchtime which ensures we can trace students’ movements throughout the school day.”
Council bosses confirmed that had been a single case at Bedale Primary School on Wednesday.
Following the confirmation of the case, North Yorkshire County Council director of public health Lincoln Sergeant said they had asked potential close contacts to isolate for 14 days, however he said parents should continue to send youngsters if they have not been contacted.
He added: “It is important to note this is not an outbreak but one positive case. We expect from time to time there will be cases affecting teachers, parents or pupils. This may reflect the background increase in cases across North Yorkshire.
“We will work with each school individually to determine the best approach to take depending on circumstances. We urge anyone who has symptoms of Covid-19, to self-isolate and book a test.
“Please note that where there are positive cases in school, families will be contacted if their child needs to self-isolate. If you haven’t been contacted, then your child is not a contact of the person who has tested positive and can continue attending school as normal.