Brentwood School in Essex confirmed the coach was carrying children aged between 11 and 13, and that one child was in intensive care after suffering a head injury.
Six teachers were also on the coach which was travelling to Cologne in Germany when it crashed into a bridge in Middelkerke, West Flanders, and shot off the road.
Pictures of the bus show it lying on its side with the front completely destroyed.
One teacher is thought to have suffered a broken collar bone in the accident that happened at around 8:45am yesterday.
The school’s head teacher Ian Davies said: “All of the children managed to walk off the coach.
“One of the children subsequently had a head injury. He had a scan and they found a small brain bleed as part of his fractured skull.”
The school is working with the Foreign Office to try to get the children home as soon as possible. A spokesman for the department said it was working with the Belgian authorities to establish details of the incident.
The school said: “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.
“Two senior members of staff have travelled to Belgium this morning and as soon as we have more information we will inform everyone involved.”
A spokeswoman for the school said other children had been lucky to escape with less serious injuries, some suffering from broken bones and cuts.
“The rest of the pupils are being looked after in a municipal swimming pool. Many of them are completely uninjured and some are even playing football,” she said.
The coach involved in the crash is owned by Richmond Coaches of Ballinderry Road, Lisburn, in Northern Ireland, and a company spokesman confirmed it only employed Northern Irish drivers.
He added that it was now trying to establish the identity of the driver and his assistant, adding: “Any incident involving a coach crash like this is clearly a tragedy.”
Local councillor Patrick Catney, who knows the family, described the crash as a “tragedy”.
“This is so sad, it’s so tragic,” he said.
“This company is very long-established and has a great safety record – they only operate top of the line luxury coaches.”
Mr Catney said his thoughts were with the family of the crash victim.
Brentwood School is a co-educational independent day and boarding school in Brentwood, Essex. Founded in 1557 and established in 1558, the school has a Tudor schoolroom, a Victorian chapel and several Grade II listed buildings.
The school is set in more than 72 acres of land in the centre of Brentwood.