An emergency response was sparked when four pupils fainted during an Armistice Day service causing a “ripple effect” through the school.
Up to 40 children felt unwell as anxiety swept through Outwood Academy School in Ripon, North Yorkshire, a senior fire officer said.
One child was treated in hospital after banging his head, possibly after he fainted.
Fire crews from across Yorkshire turned out to carry out a safety sweep of the school, with a number of ambulances and police officers.
The specialists detected no sign of carbon monoxide poisoning or any other hazardous materials.
Station manager Dave Winspear said: “Children were feeling unwell, nauseous, dizzy. The ambulance service treated children for those symptoms.
“We worked through our protocol to see if there was anything untoward and assessed the school for any hazardous materials.”
He said the emergency services did not know why the children initially felt ill, but said the hall where the 11am service was held was warm.
“We are of the view the children just fainted and there was a ripple effect throughout the school.
“More children felt anxiety and started to feel concerned and the thing has escalated.
“I would like to assure you, we have carried out a very thorough assessment and found no hazardous materials or anything untoward in the school environment.”
PA