One of the children, all aged between 11 and 13, was in intensive care receiving treatment for a head injury, the school said.
A spokesman for Brentwood School in Essex, southeast England, said the coach, which was also carrying six teachers, was travelling to Cologne in Germany when it collided with a bridge near Ostend.
The Belga news agency reported that the driver lost control on the E40 highway near the Flanders coast, sending the coach crashing into an overpass.
“All pupils walked off the coach and several pupils and teachers have been taken to local hospitals. One pupil is in intensive care receiving treatment for a head injury,” the school spokesman said.
He added: “We have been informed that the driver was killed in the collision and his assistant has been severely injured. Our thoughts are clearly with his family and all the families of the pupils and teachers involved. “