The blaze happened outside Carluke High School at 8.40am this morning (Tuesday).
More than 60 pupils got off the bus before smoke was spotted coming from the engine. The Stuarts bus then went up in flames while the pupils were walking to school.
It is understood the youngsters were forced to run during the blaze. Nobody was injured and the fire is not being treated as suspicious.
Carole McKenzie, South Lanarkshire Council’s head of education, said: “The bus was already parked when this incident occurred and the driver ensured all the pupils were safely off the vehicle after smoke was spotted.
“Nobody was hurt in this incident and the driver, school staff and pupils reacted admirably, remaining calm and working together to ensure everyone was safe.”