Teachers at a Monmouthshire comprehensive will walk out this week following concerns over some pupils' "violent and abusive" behaviour.
Staff at Caldicot School say they do not feel safe working there and were balloted about strike action in July.
The NASUWT union said its members at the school will strike on 21 and 28 September and a further four days of strikes are planned during October.
Monmouthshire council said it would keep trying to find a resolution.
A statement from NASUWT said that it had been "in negotiations with the secondary school since 2019 in a bid to resolve ongoing concerns about its management".
However it added that these talks "have failed to make sufficient progress in addressing adverse management practices affecting the health, safety and welfare of its members and the pupils in their care".
It also accused the school of "failing to provide appropriate support to staff in dealing with violent and abusive behaviour".
NASUWT general secretary Patrick Roach said: "Teachers cannot teach and pupils cannot learn in an environment where there is disruption and violence.
"Poor pupil behaviour cannot be explained away by attributing it to a teacher's ability to plan and deliver lessons appropriately - something which parents and the public accept.
