The Dulwich families have seized on the decision of Harriet Harman, the Social Security Secretary and a local MP, to send her daughter to a school in neighbouring Westminster to boost their bid.
They claim there is no suitable secondary school in Southwark for their children and that standards do not meet their expectations.
So far the campaigners have sent out more than 17,000 leaflets seeking support.
Education in Southwark, one of the ten worst boroughs in the country for GCSE results, is currently being reviewed.
Jan Barden, one of the organisers of the Dulwich Area Secondary School Campaign, said children had to travel as far as Kent or Surrey to secondary schools, or parents had to pay for their education.
"We are not trying to do down other Southwark schools but there is a lack of provision," she said.
Gordon Mott, Southwark's education and leisure director, admitted the borough was facing a shortage of places into the next century which might mean expanding existing schools or opening a new one.
"Another option might be to let the market take care of itself," he added.
Mr Mott assured families that their views would be heard.
Ms Harman and her husband, the trade unionist Jack Dromey, have decided to send their daughter Amy to the Grey Coat Hospital School in Westminster. Amy is currently a pupil at Dulwich Hamlet Junior School, in Southwark.
Ms Harman sparked controversy by ignoring party policy in sending one of her sons to St Olave's Grammar School in Orpington and the other to the London Oratory School in Fulham, also attended by Tony Blair's sons.