Jersey's government will press on with plans to build a new primary school on the former gasworks site.
St Helier Constable Simon Crowcroft was asking the States Assembly to request the government reconsiders its plans.
He wants the land used to extend the Millennium Town Park, to give people living in the island's capital access to more green space.
The site has already been earmarked for a modern primary school, which will replace St Luke's, Springfield and La Passarelle, which are deemed no longer fit for purpose.
Constable Crowcroft said the need to a new school should be reassessed because of the island's falling birth rate.
Education Minister Rob Ward told his fellow States members:
"A modern, purpose-built primary school in St Helier isn't about reacting to today's numbers, it's about planning for the next generation."
READ: Education Minister pushes back on Millennium Town Park extension
Fellow Reform Jersey member Deputy Catherine Curtis was among those who expressed concern about the ageing buildings the new school would replace:
"These schools do not have adequate facilities, and that's not fair."
Other politicians shared this view, with 31 members voting to reject Constable Crowcroft's request.
Infrastructure Minister Andy Jehan said:
"We desperately need a new primary school in town, one that is fit for purpose in the modern age and does justice to children in St Helier and St Saviour."
Economic Development Minister Kirsten Morel commented generally on States Members' attempts to throw out plans that have already been agreed on:
"Jersey's in real danger of achieving nothing at all time and time and time again."
The vote was 10 in favour, 31 against.
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