The Maidenhead Civic Society has backed campaigner's calls to abort the plan to relocate Oldfield Primary School to a new site in Bray Road.
The charity, which lobbies for positive change across the town, has about 500 members and believes alternative locations to the Bray Road site have been ignored.
Chairman of the planning group, Martin McNamee, said: "We are not convinced that the full evaluation of alternative locations has been undertaken.
"The 'only' suitable site for the construction of a new school is deemed to be the proposed Bray Road site, which very conveniently is understood to be owned by the royal borough."
About 55 protesters from Bray Action Group (BRAG) staged a demonstration outside the school on Monday to voice their disapproval of the plans.
The new school would cater for 420 children and aims to open in September next year.
It was chosen as the preferable location out of three different options.
Mr McNamee proposed the school should be enlarged at its current site and acquire land used by the Patchwork Montessori Nursery School in Chiltern Road.
He suggested the fields in Bray Road could be used exclusively for playing fields and other recreational use.
Top Ten Articles