A 15-year-old student accused of assaulting a teacher has been charged with inflicting grievous bodily harm and possession of a bladed article on education premises.
Dyfed-Powys Police said the boy has been remanded in custody and is scheduled to appear at Swansea Magistrates' Court on Saturday.
Officers were called to Milford Haven Comprehensive School in Pembrokeshire, southwest Wales, at about 3.20pm on Thursday, following a report that a teacher was assaulted by a pupil brandishing a weapon.
Police said the teacher was taken to hospital for treatment and later discharged.
All of the pupils "returned home unharmed" on Thursday, the force said, adding that the school was closed on Friday.
Detective Chief Inspector Matthew Briggs, senior investigating officer, said the force is "continuing to support the victim whilst they recover from this traumatic event".
He said the injuries suffered by the victim "have now been confirmed as stab wounds", and "there will continue to be a higher than usual police presence in the area over the coming days to provide further reassurance".
Police officers will also be "working closely with local secondary schools to offer support over the coming week", he added.
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Welsh First Minister Baroness Eluned Morgan, who had visited the school last week, said on Thursday evening that she was "deeply concerned by the incident".
"My thoughts are with the injured teacher, their family and the entire school community during this difficult time," she added.
"I want to pay tribute to the emergency services and school staff for their swift and professional response in ensuring the safety of pupils and staff.
"While this remains an active police investigation that must be allowed to proceed without interference, I want to be unequivocal... violence of any kind has no place in our schools."
The first minister also said the Welsh government will "continue to work closely with local authorities, schools and partners to support all those affected and to ensure our schools remain safe environments for learning and care".
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