Union members say planned strikes over behaviour policies at a secondary school will go ahead.
NASUWT members at St Ivo Academy in St Ives are staging the first of five walkouts.
They say teachers are having to enforce "questionable rules" which will limit their ability to manage behaviour.
The trust which runs the school said it was disappointed that the strike was going ahead but it would be open as normal.
The dispute centres on new policies being introduced at the school by the Sheffield-based Astrea Academy Trust.
NASUWT union members say the rules include:
- Having the same punishments for everything from forgetting a pen to deliberate vandalism
- Silence in all corridors at all times
- Pupils sitting in rows even during drama lessons
Talks between the academy trust and the union to resolve the issue appear to have stalled.
