“All pupils at the location are safe and most have gone home,” said Supt Neve, adding that the teacher is receiving medical treatment for their injuries.
He added that officers remained at the school, and that the 15-year-old boy was in police custody.
A Welsh Ambulance Service spokesperson said they were called to the scene and one patient was transported to hospital.
Pembrokeshire council said most pupils had now left the school and confirmed police officers remained on site.
“Any planned after-school events have been cancelled this evening,” a spokesperson said.
