The creation of a "super school" in Eastbourne is on hold after education bosses refused to back it.
Proposals to relocate Cavendish School from Eldon Road to Cross Levels Way in the town met with disapproval over the cost.
Despite increasing pressure on the education authority to find school places in East Sussex, a report before members of the county council Cabinet committee on Thursday will not recommend the scheme.
Governors of the 1,000-pupil Cavendish School hoped the relocation could provide 200 more places by 2005.
But Denise Stokoe, director of education, said: "Our conclusion is the relocation does not meet this purpose as there would be a net cost to the county council of £4 million.
"The proposed relocation would mean the majority of pupils had a significantly longer journey to school and a large part of the town would be left without a local secondary school."
Headteacher Mark Dawkins said the plans may not be scrapped completely but were on hold.
He said the school was built for 500 pupils but numbers had doubled.
Mr Dawkins said: "There has been some small-scale investment since the building was opened in 1939 but there has been a lack of funding and capital investment."
He said pupils were receiving the best education but not the facilities to match.
Work to waterproof the building was needed at a cost of about £750,000.
Eastbourne is one of the worst affected towns in the district in terms of overcrowding.
Education bosses have turned their attention to Bishop Bell School in Priory Road, which is over-subscribed.
The cost to expand the school, including the creation of a road between two buildings on the site, will be met by a voluntary aided programme, leaving the county council with a £1.6 million bill.
The education authority, under the control of the county council, will have to provide a further 140 secondary school places in the town by 2007.
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