Parents have applied for an interim injunction to halt the closure of St Bees School this summer.
The governors of the 400-year-old school had previously said it would close this year, but that they hoped to re-open it in 2016.
But campaigners say by then its long history will be destroyed and confidence in the school lost forever.
The Rescue Group which put together a package to try and save St Bees says it is now "impossible" for the school to re-open in September.
About 400 people gathered in the village church for a meeting on Saturday night.
It followed the governors' announcement on Friday that they had rejected the Rescue Group's alternative plan to secure the school's short-term future.
Rescue Group Chairman Mark George said he was "gutted" the school would not re-open in September. He added that he was "deeply sorry" the group's attempts had failed.
The under-fire chairman of St Bees' governing body, Professor Frank Woods, also attended the meeting.
He was, at times, jeered by parents and there were multiple calls for him to resign.
He said St Bees was "a treasure" but a "very expensive treasure" and that its future was not financially sustainable.
The West Cumbrian school is due to close this summer. The governors say falling pupil numbers mean it is not financially sustainable.
Governors have announced that St Bees School will close this summer.