A head teacher is worried one of his pupils could be killed if rowdy behaviour is not controlled on school buses.
David Evans, head of Blaengwawr Comprehensive School in Aberaman in the Cynon Valley, says children from his school are so badly behaved there could be a tragedy.
He wants supervision on bus trips to and from the school, and the council has agreed to look at the problems.
His warning follows the inquest which reached an accidental death verdict on the death of 12-year-old Stuart Cunningham-Jones, who died when the bus he was in hit a tree near Ystradowen in the Vale of Glamorgan in December 2002.
An inquest earlier this month heard how the bus driver was distracted by pupils "messing around " by his cab. Two boys were fighting and, as one fell, he reached out and touched the steering wheel.
Speaking to BBC Wales on Friday, Mr Evans said he had received numerous complaints about his pupils' behaviour on trips to and from school - particularly those travelling on the top deck.
"Parents of our children, parents of younger children, residents, governors - you name them - there have been complaints from them all, and they are entirely justified," he said.
"Pupils are completely unsupervised and that is the same as putting them into a classroom without a teacher and telling them to write an essay.
"Pupils have been hanging out of the back of the bus - literally hanging out of the back. I am concerned someone could die."
Drivers from Shamrock Coaches, who operate the school service, have told Mr Evans some worrying stories about disruptive behaviour on board.
Last week one driver, Paul Griffiths, reported an incident on a single-deck bus he was driving with Blaengwawr pupils on board.
"They were sat on the roof of the bus when I was driving, and when I stopped, they jumped off onto the pavement," he explained.
"The roof slides back, and they just jumped up and out. If I had had to brake hard, they would have been off the top.
Boys had been fighting on the bus before Stuart Cunningham-Jones died
"If they had fallen into the path of oncoming traffic they would have died.
"That's why I believe there should be minders on all the vehicles. We can't drive and watch the children the same time."
Fellow driver Rhydian Williams said he had had similar experiences.
"They have been opening the back emergency window, there have been pupils hanging out the back - it's terrible," he said.
Shamrock Coaches and the school have put their concerns to Rhondda Cynon Taf council, but have been told that supervision will not be provided.
But David Bishop, director of environmental services at the council, said he would be looking into the problems and that everyone had a role to play.
"We will be taking some active steps over the next couple of weeks to really get to the bottom of the problem at Blaengwawr," he said.
"We need to understand what is going on there, and try to deal with the issue to ensure safety for the passengers, and then think if there are any longer-term implications for this particular school."
On Wednesday it emerged that CCTV cameras were to be tested on school buses in west Wales.