Dyfed-Powys Police said the 15-year-old 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 the Pembrokeshire region of south-west Wales at about 3.20pm on Thursday, following a report that a teacher was assaulted by a pupil brandishing a weapon.
The teacher was taken to hospital for treatment and later discharged.
The school was closed on Friday and police said all of the pupils “returned home unharmed”.
Following the incident, the Welsh First Minister said “violence of any kind has no place in our schools”.
Baroness Eluned Morgan visited the school only last week and, on Thursday evening, said in a statement shared on social media: “I am deeply concerned by the incident at the school in Milford Haven. Having visited the school only last week, this news is particularly shocking.
“My thoughts are with the injured teacher, their family and the entire school community during this difficult time. 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.”
She added: “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.”
Senior Investigating Officer, Detective Chief Inspector Matthew Briggs said there would be a higher than usual police presence in the area over the coming days to provide further reassurance, adding: "Officers will be working closely with local secondary schools to offer support over the coming week”.
