Three hundred pupils, parents and staff converged on Lewisham town hall last week in a bid to stop their school from becoming an academy.
Sedgehill in Catford, faces having its governors removed by Lewisham Council and replaced with an interim board after refusing to allow for an academy principal to become executive headteacher following an Ofsted report showing it requires improvement.
If the partnership went ahead, Sedgehill would need to consult on becoming an academy.
But on Friday, an after-school protest saw a mass of singing, chanting teenagers and their parents make an extraordinary protest outside the town hall in Catford, with banners imploring the council to ballot parents and "save Kenzy" - a reference to head teacher Ken Mackenzie.
Former councillor Gurbaksh Garcha, whose three grandchildren go to the school, said he had never seen a campaign like it in Lewisham.
He said: "The parents, the governors, the pupils are absolutely solid. The head is worshipped here.
"To take on a community like that is foolhardy. The council represents this borough and these are the people."
A group of students got the loudest cheer of the evening as they made their way inside to deliver a 1,500-signature petition to cabinet member for schools Councillor Paul Maslin.
Nineteen-year-old former pupil Damali Eastmond-Scott, who handed it over, said: "Just being part of the Sedgehill community is so powerful."
The Manchester University student said: "People should be given the chance to go to a place like Sedgehill, not an academy. It's so much more than just an exam machine."
Campaigners say the school is improving, doing better than some of its neighbours and fear an academy would bring increased pressure to improve exam results rather than helping "the whole child".
Mum-of-three Leanne Garcha said: "No letter of the alphabet can describe how well my child is doing."
The 43-year-old, of Rockbourne Road, Forest Hill, said: "The school is improving day by day. It's not failing. We don't want a hostile takeover. It's a real family. Sedgehill has a massive heart and they're going to destroy it."
Campaigners also point out that the council tried to install an academy head teacher back in 2010 and was foiled by the governors.
In a lengthy statement, a spokesman for Lewisham Council said: "If we were to accept the governors’ preferred course of action, to strengthen the existing partnership arrangements at the school rather than to take on a new partner, it is highly likely that the school would face a further Ofsted inspection.
"Because we know that Ofsted has serious concerns about the school, this further inspection could lead to the school being placed in special measures. The Department of Education would then intervene.
"We believe that the course of action we have chosen gives the best chance to keep Sedgehill within the Lewisham community of schools and to play its part in giving our young people the best chance to succeed in life."
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