Police also confirmed that the teacher sustained stab wounds, after an initial assessment described “non-stab injuries”.
“There will continue to be a higher than usual police presence in the area over the coming days to provide further reassurance,” Det Ch Insp Matthew Briggs said.
All school events were cancelled following the incident on Thursday, with the school remaining closed on Friday but available for those requiring additional support.
Following the incident, Wales First Minister Eluned Morgan said “violence of any kind has no place in our schools”.
Morgan, who visited the school last week, said her thoughts were with the injured teacher, their family and the entire school community, adding her government would support all those affected.
Matt Wrack, the general secretary of the NASUWT teachers’ union, said schools “should be places of safety and learning – not fear and violence”.
“We will be standing by to offer all the support we can,” he said.