Both the tractor and the school bus were heading east on Hackman Road near Runge Road when the accident happened around 7:25 a.m., CHP Officer Chris Parker said.
Witnesses said the tractor was traveling at about 20 mph with its hazard lights on and the bus was traveling behind the tractor at about 35 mph, Parker said.
The bus driver crossed a solid yellow line to pass the tractor as it approached Runge Road, Parker said.
However, as the bus passed it, the tractor began to turn left onto Runge Road and the right front end of the bus struck the left rear tire of the tractor, Parker said.
The bus rode up onto the tractor's tire and overturned onto its left side, Parker said.
All the children on the bus were wearing seat belts, which prevented more serious injuries, Parker said.
The bus driver suffered minor to moderate injuries and was taken to a hospital. The driver of the tractor was not injured, Parker said.
Parker did not yet know the ages of the children, the school they were heading to or the identities of the drivers.