Teachers at the biggest secondary school in Derbyshire are staging another one-day strike over plans to turn the school into an academy.
About 60 staff at the 2,200-pupil John Port School in Etwall are on strike.
Pupils from Years 10, 11, 12 and 13 will attend school but the remaining 1,400 will have the day off.
The school has been given the go-ahead for academy status but head teacher Wendy Sharp said no decisions had yet been made.
In a letter to parents, Ms Sharp wrote: "The governors and I are working closely with the local authority to gather accurate and pertinent information so that we can make the wisest decision for John Port School and all its stakeholders."
The school said conversion to an academy would mean £1m of extra funding, but teachers are worried about changes to pay and working conditions.
Chris Lines, president of the National Association of Schoolmasters Union of Women Teachers (NASUWT), said: "We are doing this to protect state education - which we believe should be democratically responsible to the community where the school is.
"We are showing the community and the governors the staff are firmly in favour of remaining within the local authority family of schools."
Academies are funded directly by the government and not via the local authority.
The walkout follows a one-day walkout on 10 February and two one-day strikes over the same issue by the NASUWT at Ecclesbourne School, Duffield, in January.
John Port School and 14 other schools in Derbyshire want to convert to academies outside local authority control because they believe it will help them gain more government cash.
Chellaston School in Derbyshire converted to an academy on 1 December and Kirk Hallam Community Technology College intends to change over on 1 March.