One teenager is in hospital with stab wounds to the chest while another is in police custody after an apparent classroom fight in Nowra.
Police have charged a 13-year-old boy over the stabbing at Shoalhaven High School in Nowra.
The 14-year-old victim suffered a punctured lung and is in a serious condition in hospital after he was stabbed in the chest in a classroom about midday on Monday.
Police were told the injured boy had been in an argument with another student before being assaulted.
The Department of Education said the school was working with local police after the incident between two students.
Police initially arrested a 14-year-old boy in the classroom and took him to Nowra police station but they later released him without charge.
A 13-year-old boy then attended Nowra Police Station with his mother, where he was questioned and charged with wound with intent to cause grievous bodily harm.
The boy was refused bail to appear in court on Tuesday.
Inspector John Behrendt, from Nowra police, said the victim was stabbed in the left side of his chest.
He said he believed the boy had been stabbed in the classroom.
The victim was taken to Shoalhaven Hospital and then transferred to Sydney's Children Hospital, where he remains in a serious condition. His injuries are not considered life-threatening.
The Department of Education and Communities said it could not make further comment as the matter was under police investigation.