It started out as a friendly tussle between two schoolboys during recess, but soon turned into a scuffle.
One slashed the other with a paper cutter, leaving a 4-cm cut at the back of the head.
The 13-year-old boy was still bleeding when the Singapore Civil Defence Force arrived at the school.
He was later sent for treatment at KK Women’s and Children’s Hospital.
The school said that the parents of both students have been informed of the incident. Both students have also been counselled.