Natasha Paton, 17, died after a coach carrying 39 pupils and five members of staff from Lanark Grammar School crashed in wintry conditions.
The bus was going to Alton Towers theme park when it smashed through a bridge and went into a river near Biggar in March 2010.
However, Natasha's relatives have reacted angrily to a report by the Traffic Commissioner for Scotland which found "no evidence pointing to failings by the operator".
A statement issued on behalf of the Paton family said they had been left distressed by the claims.
David Wilson, of Digby Brown solicitors, said: "This has caused stress and anguish to the family.
"The Fatal Accident Inquiry into Natasha Paton's death was very clear. Responsibility for the crash lay with the driver of the coach. The driver was working for the coach company in question at the time of an accident that resulted in a tragic death and left at least 32 others injured.
"The lawyers for the driver have admitted in open court primary liabilty for the crash that caused Natasha Paton's death."
Traffic Commisioner Joan Aitken had called Carluke-based James Purdie and Kenneth Purdie, who trade as Photoflash Services, to a hearing in Edinburgh after an investigation by the Vehicle and Operator Services Agency.
Ms Aitken was told the necessary systems were in place and satisfactory but with some minor shortcomings.
The Driver and Vehicle Standards Agency evidence did not point to fault on the part of the operator in the lead up to the crash.
Ms Aitken issued a warning about improvements required by the business, but said these would not have prevented the crash.
Last year, a Fatal Accident Inquiry found Natasha's death could have been prevented if she had worn a seatbelt and the driver, Raymond Munro, had gone slower.
Sheriff Nikola Stewart, who oversaw the inquiry in March 2010, released her findings in May last year.
She heard Mr Munro lost control of the vehicle. After the coach collided with the bridge Natasha was thrown from the vehicle and drowned in the water.
Sheriff Stewart said Natasha, of Cleghorn, may have lived if the driver "had travelled at a lower speed on the approach to and turn on to Castledyke Bridge and refrained from applying the brakes while negotiating that turn".
The sheriff said Mr Munro could also have refrained from attempting to negotiate the turn on to the bridge at a speed of 23mph or more.
All passenger seats were fitted with lap seat belts and teachers had checked pupils were wearing them before the coach set off.
At least nine pupils, including Natasha, were not wearing seat belts at the time of impact.
Natasha's family are suing the driver for damages at the Court of Session in Edinburgh. No date has been set for the hearing.