Teachers at Weston Favell school in Northampton struck on Thursday of last week in protest at plans to turn the school into an academy.
The strike brought together members of the NUT and NASUWT unions in opposition to the academy plans.
Around 50 teachers and sixth formers picketed and demonstrated outside the school. They were joined by delegations from local Unison, UCU and CWU unions.
Northamptonshire county council wants to remove the school from local authority control and hand it over to the disgraced United Learning Trust (ULT).
Sarah Ansell, president of the Northampton association of the NUT, said that strikes “will not damage children’s education in the longer term in the same way becoming an academy would”.