The assistant driver was killed when a bus carrying 34 children from Britain overturned on a Belgian highway early on Sunday, a local official said.
None of the children were seriously injured when the driver lost control of the bus on the E40 highway near the Flanders coast, sending it crashing into an overpass, Belga news agency said.
Some children and their monitors suffered minor injuries and were evacuated to a local hospital.
The principal driver meanwhile remained in a serious condition, authorities said.
The children were aged 11 to 13, according to British media reports.