TEACHERS belonging to the NASUWT in the Derry City and Strabane are staging a one-day strike over pay, jobs and workload.
A number of schools in those areas are closed or partially closed to pupils today.
The outgoing Education Minister Peter Weir had previously called the strike “futile”.
The NASUWT union said it had been “forced” into the action.
Meanwhile, the union representing many school principals said that industrial action was having a “profound impact” on school inspections.
In October, all five main teaching unions in the North of Ireland rejected an offer that would have seen their pay frozen last year and a rise of 1% for 2016-17.
Members of the NASUWT in Belfast and Newtownabbey subsequently held a one-day walkout last November.
Teachers belonging to the INTO union also staged a earlier this month.
Schools had already informed pupils and parents about Tuesday’s planned closures.
Members of the other classroom teaching unions – the Ulster Teachers’ Union (UTU) and Association of Teachers and Lecturers (ATL) – voted against strike action.
However, all of the classroom teaching unions are also taking action short of a strike.