The yobs set light to the bus after scaling a fence to get into the grounds of Cordwalles Middle School on the town's Old Dean estate.
Eyewitnesses saw a group of children, aged 12 to 13, running away from the school shortly before the vehicle went up in flames at about 11.20pm last Friday.
Fire crews attended the blaze but were unable to prevent the minibus, valued at £5000, being reduced to a burnt out shell.
The arson is the latest in a wave of incidents of vandalism which has hit the school in recent weeks.
Headteacher Mrs Michele Knight said on Monday: "This was a deliberate act of vandalism which is going to have a big impact on the children."
Among the first to be affected are seven physically disabled pupils who attend a special unit at the school. They were looking forward to a special day out in the minibus yesterday (Wednesday) organised by the local Rotary Club.
Mrs Knight said: "Now they don't know if they will be going. It's so disappointing for them."
The loss of the minibus also threatens to put paid to several other trips lined up for the school's 288 pupils during the summer term.
She said the spate of vandalism was threatening to damage staff morale, and it was draining the school's budget. There have been eight cases of windows being smashed at the school during a recent 10-day period.
After one attack it was impossible to board up all the windows, so a security guard was called in for an overnight patrol - at a cost of £22 an hour.
Each insurance claim includes an excess figure which has to be paid by the school. In the case of the minibus it will be £2000.
Mrs Knight, who feared the school would not be able to afford to buy another minibus, said: "Everyone is fed up and quite despondent…it's very hard on the staff.
"I have written to parents asking them to be vigilant and to contact the police if they have any information about the vandalism, and I have spoken to the children."
Mrs Judy Williams, Camberley police press officer, said on Monday that two juveniles had been arrested on suspicion of arson. They have been bailed pending further inquiries.