Pupils have accused a driver of ordering them off the school bus and leaving them stranded miles from home.
Burford School and Community College pupil Zoe Amos, 16, claims the driver left more than 80 students -- some as young as 11 -- at the roadside in Brize Norton on the journey home from school on Friday.
But bus company Angela's Travel said the children walked off themselves through the emergency exit when the driver tried to drive back to the school after a window was smashed.
The company, which is contracted by Oxfordshire County Council, said trouble occasionally flared up on the 106-seater double-decker, with five windows smashed during the past two years.
Headteacher Patrick Sanders, who is investigating the incident, criticised the lack of adult supervision on large school buses, saying drivers needed more support.
Zoe, who lives in Bampton, said: "We were on the way home when one of the boys tried to open a window. It broke and the bus driver told us he would have to take us all back to school. "The next thing we knew, he stopped and ordered everyone off the bus. We all got off and then he just drove off.
"Kids as young as 11 were left on the side of the road and had to walk up to four miles home. Some people's parents could pick them up but a lot were still at work.
"The bus is in an awful condition and it's often late. We want something done about it. I've got my GCSEs starting this week and I'm worried that I might not get to my exams on time if the bus service continues to be this unreliable. I'm really angry and so are my parents."
But Angela Williams, owner of Angela's Travel , of Minster Lovell, said: "They were not told to get off the bus. My driver phoned me after the window was smashed and I told him to take the bus back to the school to report it.
"He told the pupils he was going to take them back to the school and they just legged it.
"If this had been the first time a window was broken I would have let it pass, but it's happened five or six times in the past two years.
"There are no problems on the buses usually, but every so often the Bampton bus flares up. It's usually just a few pupils. We're only interested in the safety of the children."
Mr Sanders said: "The pupils are feeling very aggrieved that they were left to find their own way home.
"We have more than 800 pupils transported to and from school and the only problems are on the very large double-decker buses.
He added: "I don't think it's reasonable to ask a driver to drive a bus safely and be responsible for the health and safety of 106 pupils."
County council education spokesman John Mitchell said: "From our point of view this incident seems to have been dealt with appropriately.
"In terms of having more supervision on school buses, we have to strike a balance between what might be ideal and what we can afford."
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