The proposals to build a new school on the site of the present Myers Grove site at Stannington, merging it with Wisewood Secondary, have provoked a storm of protest from thousands of parents and residents in the area.
But their campaign is also being closely monitored by members of the National Union of Teachers all over the country.
The union's general secretary Steve Sinnott has already sent a personal message of support to the protesters and letters backing their stand have also been sent from branches across the country.
If the merger goes ahead, the city council will have to decide whether it wants to run the new school itself or let a private company or charity take it over.
If councillors want to administer the school, a decision will be made by an independent panel who will be told to favour "diversity" - in other words, alternatives to local authority control.
The other option is for the council to back out and let outsiders bid for the role unhindered. Sheffield is one of only four cities which will pilot trust schools, and the battle over the future of Wisewood and Myers Grove is one of the first of its kind to raise the issue.
Sheffield's branch of the NUT holds its annual general meeting on Monday and members are being asked to openly back the protesters.
Teacher John Ross will argue the proposals have national significance and represent an important test case for the union.
"The proposals threaten the pay and conditions of teachers in both schools as they would be taken out of local authority control under trust status," his motion says.
"They will also have to reapply for their own jobs. Trust schools are unaccountable - the involvement of bids to run trust schools by private companies and businesses amounts to the effective privatisation of local schools," it adds.
Sheffield NUT secretary David Tucker said the concern was that trust schools were seen as a less democratic and accountable form of education.
He added: "We also believe the Government rules which will decide this issue in Sheffield are somewhat biased - they are rigged in favour of trusts.

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