Pupils at St Mary's Catholic High School in Leyland were evacuated after an electrical fault sparked an emergency, say fire services.
Four fire engines were called out to the premises on Royal Avenue at around 9.30am on Monday, January 29.
Crews say that an electrical fault in an oven at the school started a small fire which was out by the time they arrived.
A spokesman for the fire service said: "We sent four appliances to the school to reports of a fire in an oven.
"The school was evacuated and the fire was already out by the time we arrived.
"We believe the fire started as a result of an electrical fault."
Nobody was injured and no damage was caused as a result of the fire.