Less than a year after the introduction of laws requiring school buses to fit seatbelts, only one in 10 pupils is belting up, according to bus company research.
But drivers won't make pupils wear the belts because a legal loophole means they face compensation claims if passengers are injured by belts worn at their insistence.
Mike Bartlett of the Confederation of Passenger Transport, an association of bus and coach companies, said his members found themselves in a "legal minefield".
Their own research showed that, although use of seatbelts was more frequent on supervised school trips, about 90 per cent of pupils did not belt up on unsupervised trips to and from school.
But the risk of legal action meant companies could do little about the risks being taken on their vehicles. "We have advised members that they should make passengers aware of seatbelts, but that they should not even suggest they be worn, because of the risk of claims," Mr Bartlett said.
Margaret Morrissey, of the National Confederation of Parent Teacher Associations, said school bus services were "in a mess".
"What price a child's life?" she said. "It is not satisfactory to have only 10 per cent of pupils using belts. We should have transport with supervision by an adult - and that supervision should not be by the bus driver.
"At the moment, we are asking drivers to drive a bus safely and to supervise large groups of pupils at the same time," she said.
Roger Vincent, of the Royal Society for the Prevention of Accidents (RoSPA), echoed the call.
RoSPA had been campaigning for compulsory wearing of seatbelts before the death of 12 pupils and a teacher from Hagley High School, Stourbridge, in a minibus crash highlighted the issue in 1993. But it was important not to expect drivers alone to enforce such regulations.
"On this sort of transport there should be an escort provided by the school, charged specifically with looking after the kids. At home, there is also a job to be done in convincing pupils of the importance of using belts," he said.
Mark Hayball of Beeline Coaches, which runs school bus services in Warminster, Wiltshire, said that problems varied.
"Generally we find junior- school pupils wear them because their mums tell them to. The secondary pupils are the ones that don't," he said. "It might be a fashion statement, it might be that we aren't getting through to them about why they should wear belts - but they've got their minds on their girlfriends or boyfriends, or on their GCSEs, and they don't want to bother."