The overturned coach was carrying 47 pupils and staff from St John Rigby Sixth Form College, Orrell, Wigan. They were returning from a trip to Alton Towers to mark the end of their exams.
The driver was trapped and had to be released by firemen, while the driver of the other coach, which was empty, was also seriously injured.
It was not immediately known whether the coaches were fitted with rear seat belts. If not, there will be renewed calls for belts to be fitted to all coaches and minibuses.
The accident happened at 6.50pm yesterday as both vehicles were travelling north on the M6 between junctions 16 and 17, just past the Sandbach service station turn-off.
The coach carrying the students was travelling behind the empty coach which is thought to have braked suddenly to avoid a heavy goods vehicle. The empty coach stayed on the motorway while the school coach went up the embankment and overturned.
Two students suffered head injuries, one serious. One had a back injury, and three were suffering from shock.Reuse content