Brandon Strain did not suffer any physical injuries, but he told his mother, Rebecca, that he didn't want to take the bus again.
Brandon also was having difficulty Tuesday letting his mother out of sight, Rebecca Strain said.
"I hope this doesn't have long-term effects on him," Strain said. "It shouldn't have happened. . . . Why didn't they see him sleeping?"
The Alpine School District was investigating the incident and will take appropriate action, said District Super- intendent Vern Henshaw. Utah County sheriff's Sgt. Spencer Cannon said there was no suspicion of wrongdoing.
Henshaw said it is school district policy to check buses after all the children exit.
"Obviously, something's taken place that's really serious," said Henshaw.
Strain put Brandon on the bus at about 8:45 a.m. The bus driver finished the route and parked at the school district's bus garage.
Around 1:25 p.m. the driver returned to the bus for her afternoon route and found Brandon still aboard, Cannon said.
The driver was accompanied by an aide, and it was unclear why they didn't see the boy after the morning route was finished, he said.