Twelve children and one of the drivers were taken to hospital after the crash between two double-decker school buses between Rothwell and Desborough, police have confirmed.
The crash happened at 3.30pm today, Tuesday.
In a statement released at 6.30pm, a spokesman for Northamptonshire Police said: "All of the casualties involved in the incident have now left the scene.
"There were 27 children who sustained minor injuries.
"Eight were taken to hospital by ambulance with four taken to hospital by their parents.
"The rest have been discharged home from the scene.
"One of the drivers was taken to hospital," he said.
All casualties were taken to Kettering General Hospital.
Roads remain closed in both directions while recovery of the vehicles takes place and repairs are made to the road.
Any witnesses to the incident or anyone with dashcam footage can call Northamptonshire Police on 101.