Teachers are set to take strike action at a school in Lincolnshire in protest over working conditions.
Teaching union members from King Edward VI Grammar School in Louth will walk out six times, starting on Thursday.
Dr Patrick Roach, General Secretary of the union NASUWT, said the expectations on teachers at the school were "simply not sustainable or fair".
The school's head teacher James Lascelles said they were working hard to address the concerns.
The strike action has been called due to concerns over the school's "enrichment programme" - described as an opportunity for students to gather at the end of the teaching day and take part in activities such as sport, debating, drama and music.
However, Dr Roach said: "The current structure of the school day is eroding time to teach the curriculum and undermining opportunities for pupils to learn.
"Exhausted and stressed teachers cannot deliver the best standard of learning to pupils," he said.
"We urge the employer to recognise the need for change and agree to work with us in the best interests of both staff and pupils at the school."
In response, Mr Lascelles said the school had listened "carefully and patiently" to the concerns raised and had proposed removing the enrichment activities from the timetable after the February half-term break and from the 2024/25 curriculum.
"We understood this met the concerns raised," he said.
"We were therefore very surprised, and disappointed, that teachers decided to reject the offer."
