Several children are believed to have been hit when plastic pellets were fired from the toy gun by fellow pupils of St Nicholas' High School, in Hartford.
The incident happened last Thursday afternoon as a county council education bus was transporting pupils from the Greenbank Lane school to their homes in Winsford.
One furious parent, who wishes to remain anonymous, told the Guardian: "My 13-year-old son was on the bus and thankfully he wasn't hit, but he could have been seriously hurt.
"He is very, very scared by what has happened and keeps having terrible nightmares."
It is not thought any of the children were seriously injured as a result of the incident.
But a spokesman on behalf of the school and Cheshire County Council, said: "Both the authority and the school feel this sort of action is not acceptable and we do not tolerate any conduct which causes disruption to the driver of the bus, or anything which could possibly endanger the safety of pupils and other road users.
"The pupils concerned have been suspended from school for eight days and their bus passes withdrawn until Easter."
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article