One in four of nearly 600 buses used to take children to and from school have defects, Real Story reveals.
The number of defective school buses has risen
One in 15 where so bad they were ordered off the road immediately, according to the government survey.
Linda Howard, of First Bus, tells the programme there is no excuse for using the vehicles that are not road-worthy.
"Poor school transport can kill kids at the end of the day," she says.
"There are more regulations to transport animals to an abattoir then transporting kids to school," she says.
The programme also finds out that the DVLA may introduce new checks for all UK bus drivers following several cases of sexual assaults on children.
There have been more than a dozen cases in the UK in the last three years where school bus drivers have sexually abused children.
Real Story gained exclusive access to the government's annual Operation Coachman campaign, involving unannounced checks on vehicles, to monitor the safety of school buses.
More than 140 (25%) of vehicles had some sort of fault, the report shows. That's 6% more than last year.
Ch Supt Anwyl, who was involved in the operation, says: "Tyres were defective, too dangerous for those vehicles to be able to continue their journeys.
"We have basic defects - these are quite dreadful defects."
One in 15 buses inspected had such serious defects they had to be taken off the road immediately.
"The increasing age of the fleet means that it's only a matter of time before something catastrophic happens and there's a serious injury," says Ch Supt Anwyl.
The results come as no surprise to Pat Harris. She's campaigned for better school transport since her son was injured in a road traffic accident.
"There are far too many cowboys still transporting children to school," she says.
"The horror stories have come my way are buses that have had bolts on the outside of the emergency exits to stop the children from misusing it, corrosion in the roof supports, bald tyres, holes in the floor, fumes coming up, seats that actually move.
"Hundreds of children are travelling every day on vehicles where they are at risk."
Real Story: BBC One, Monday, 10 July, at 1930 BST.