Whangarei Boys High School has suspended a pupil after a classmate's skull was fractured in an unprovoked attack on Wednesday.
The victim, 14, was attacked while taking tests in the school hall and is in hospital with a broken brow bone, a broken nose and concussion.
School principal Al Kirk describes the attack as a random act of unexplainable violence.
Police say the accused will be dealt with in the Youth Court.
