Police spokesperson Malcolm Pojie said the three arrested pupils were between the ages of 16 and 18, in grades 8 and 12.
They will appear at the Mossel Bay Magistrate’s court on Monday.
The incident occurred during the first break, when the group of boys allegedly attacked the deceased several times with sharp objects, Pojie said. On his way to the principal’s office, Ndanda had collapsed.
He was rushed to hospital and died as a result of his injuries.