Youngsters at the Brimsham Green comprehensive rely on the specially-adapted bus to take them to various activities.
But it has gone past its best-before date and, at 14 years old, has started to become unreliable.
When some of the special needs pupils travelled to the national finals of a table cricket competition – played on a table tennis surface using special bats and balls – at Lords cricket ground last year, the bus broke down in Hammersmith and the children had to be taken out in their wheelchairs to await the arrival of the AA.
The breakdown man who got them back on the road and to Lords said the fault was caused by old age.
But a replacement vehicle will cost £40,000 and although the school has won the support of the Variety Club, it needs to raise as much money as possible itself.
Brenda Oxford, lead teaching assistant at the Brimsham Green School Resource Base for special needs youngsters, said: "We use the bus to take the children to such things as swimming lessons, sports events, on residential visits and field trips.
"Fundraising has been quite difficult but so far it has brought in £4,000 through events such as cake sales. But the more we collect, the quicker we hope we can get a replacement.
"We are now organising a big auction event for February at the Compass Inn in Tormarton and are appealing for donations of items from individuals, organisations and companies."
The bus will have to be modified to allow wheelchair access, as well as being fitted with a hoist. It will be provided through the Variety Club, which will give money to go with that raised by the Yate team.
The auction night will take place on Friday, February 26, and anyone who wants to make a donation should contact the base on 01454 868888.