East Dunbartonshire Council proposes to shut St Joseph's in Milngavie and merge it to create a new school on the site of St Andrew's in Bearsden. But protesters said figures released under the Freedom of Information act show the primary is flourishing.
And they have developed their own alternative plans to closing the school.
Laureen McIntyre, chairwoman of St Joseph's Parent Council, said: "St Joseph's Primary has been at the heart of the Milngavie community for well over 100 years.
"We are the fastest growing school in the whole of East Dunbartonshire and we want to stay where we belong."
Figures passed to the school's parent council show the roll at St Joseph's has increased by 26.6% in the past year, the highest of 50 East Dunbartonshire schools.
The Keep St Joseph's, in Milngavie campaign group has published an alternative proposal document outlining a series of options.
Plans include creating a new campus in Milngavie and combining health and community services on the site.
Laureen added: "We were very disappointed when the council ignored Archbishop Tartaglia's personal plea earlier this year for them to bring forward alternatives to closure, but we have used the time over the summer to do the job ourselves.
"A shared campus or a community hub would be a very popular option for the whole of Milngavie. East Dunbartonshire Council has been forced to admit that a shared campus would produce savings of almost £100,000 a year. We are offering them a solution."
Gordon Currie, East Dunbartonshire Council's head of education, said: "Despite an increase in the roll over the last three years, it is currently 52% under occupied and forecast to remain so for the next decade.
"I have been sent a copy of the Alternative Options Paper, produced by the group and will of course read it thoroughly. During the statutory consultation process there will be an opportunity for all views and suggestions to be aired."
Paula Speirs, the management consultant behind the new proposals, added: "Our paper is intended to show there are alternative options available to the council."