Dozens of demonstrators lobbied education chiefs to ensure work on a school described as "falling apart" takes place.
Parents and children are angry at the state of the school
Parents, pupils and supporters of Cowbridge Comprehensive Schoolgathered at the Vale of Glamorgan council offices in Barry on Wednesday.
It came as the council's cabinet held talks about the redevelopment of three schools including Cowbridge.
The council approved the School Investment Strategy at the meeting.
And made Cowbridge Comprehensive a priority.
The multi-million pound strategy described as an "immense challenge" will see Cowbridge, St Cyres and Llantwit Major schools being redeveloped or rebuilt.
Speaking before the meeting, cabinet member for education and lifelong learning, Nigel Gibbs, said: "The delivery of the strategy is one of the key priorities of the council.
Broken steps to a classroom fire exit are among the repairs needed
"The report being considered by Cabinet is the latest stage of a great deal of work by officers and members of the council and is good news for schools in the Vale.
"A technical appraisal of the options has been completed, and cabinet will be asked to agree the recommendation of the director of learning and development to progress Cowbridge School as the first priority," he added.
Pupils at Cowbridge Comprehensive have claimed it suffers from run-down classrooms, waterlogged playing fields and an infestation of rats.
Mel Massey, a schoolgirl from the 1,400-pupil site recently revealed the "awful conditions" in a film she made as part of a BBC Wales website project.
Pupils urged education bosses to say when the repairs would happen
And now parents, pupils and supporters are starting a campaign to get the repairs they say are vital for the school.
Matt Holloway from the school's PTA said the situation was "frustrating".
"We want to be supportive of the council but we've been hanging around for 35 years now," he said.
"There's been stories about a new school for Cowbridge since the 1970s.
"We've heard all the promises before but now it's time to do something about it."
He said although there had been "positive vibes" from the council about the planned redevelopment of the school and two others in the area, no time scale had been set.
"We are not going to stand back and let this fade away," he said.
"It's gone onto another generation and things are worse now than ever."
He said the school had rat infestations and areas of the building had been cordoned off because it was not safe for pupils and teachers.
"If you talk to the kids, they feel as strong about this issue as the parents," he said.
"The teachers are incredibly frustrated about it too."