Monk's Walk School said, on their Facebook page, that participants were advised by the NHS' 111 service to stay inside as a "precautionary measure".
They added, yesterday, that: "Some, but not all of this number have been told they will receive an appointment for a swab test.
"The appointment could take up to three days to come through.
"There remains no confirmed cases of coronavirus and the advice for parents and carers remains the same."
On behalf of the school, a Herts County Council spokesperson said: "The school is open as usual and we are following all the latest advice and guidance from Public Health England."
"Dear Parent/Carer
Further to yesterday’s update, today we have had further details passed to us of ski trip participants being advised by the NHS111 service to self-isolate as a precautionary measure, this bringing our total number to 5. Some, but not all of this number have been told they will receive an appointment for a swab test. The appointment could take up to three days to come through."