Parents said they had 'no idea' what was happening
Parents at the school in Devon attended by a 12-year-old girl who contracted swine flu have expressed frustration at learning the news from Gordon Brown.
Paignton Community and Sports College will be closed until 11 May to stop the spread of the virus.
The Health Protection Agency identified that the girl had been in contact with 50 fellow pupils and others.
But parents said they had not been aware of the outbreak until it was confirmed in the House of Commons.
The BBC's Alex Bushill said parents arrived at the school were "shocked and surprised" to find it surrounded by television camera crews.
'Reeling from shock'
"In amongst the tears, parents came to collect their children as the school was closed.
"Reeling not just from the shock that swine flu had arrived on their doorstep, but in the manner that they had heard the worrying news," our correspondent said.
Lisa Walton, 36, who has two sons, Liam and Jack, at the school, said: "We just had no idea about what was happening here. The school had not told us about it, and my son said the pupils were told around 1300 BST today.
"Right now we just don't know what to think. Obviously it's a worry."
As a precautionary measure anti-virals have been given to 230 pupils, the whole of the infected girl's school year.
A statement issued by Torbay NHS Care Trust said the pupil "has already responded well to treatment" and is in isolation at home.
She returned to school last Wednesday and developed mild flu symptoms at the end of last week.
Dr Sarah Harrison, consultant in public health for Torbay Care Trust, said: "We are keen to reassure the local community that only those who have had close contact with the student need to be offered anti-viral drugs."