The Children and Young Persons Bill will pave the way for six to nine pilot practices to be set up, in a bid to improve the care offered to looked-after children.
The practices would mirror professional partnerships such as those of doctors and lawyers, with six to 10 partners per practice. The majority would be social workers.
They would also be autonomous organisations, run by a charity or private company, operating to contracts awarded by local authorities.
The idea has been recommended by a government advisory group headed by Professor Julian Le Grand, from the London School of Economics. Ministers believe it could lead to better relationships between looked-after children and social workers, with more continuity and less bureaucracy. But opponents say the practices would create a more fragmented service.
Opposition and cross-bench peers want to see the scheme struck from the bill and have attacked it recently in the House of Lords.
Now heads are also expressing their worries. John Dunford, general secretary of the Association of School and College Leaders, said: "It would be better to make what we already have work. There aren't enough social workers to go round as it is, and this could just make things worse."
His comments came a week after two studies revealed that schools' relationships with social workers are already under pressure.
The Every Child Matters agenda means that schools and social workers are supposed to work closely together to improve the protection offered to cared-for children.
But a survey by the National Foundation for Education Research found that only 27 per cent of secondary and 41 per cent of primary heads rated their school's accessibility to social services support as excellent or good.
One secondary head said there was a "real culture clash between education and social services."
Meanwhile, an ICM poll for The Guardian found that 56 per cent of heads said social services did not communicate well with their schools. The same proportion thought it was unacceptable for schools to have more of a social services role, with 45 per cent saying they would feel the same way even if they had more funds.
Social work practices have been strongly opposed by peers, inspired by a personal pamphlet written by Chris Waterman, executive director of the Association of Directors of Children's Services.
Baroness Meacher, a crossbench peer and qualified social worker, was particularly critical of the idea that contracting the support offered to looked-after children outside local authorities would solve problems like bureaucracy. "The reality is that whether the bureaucracy shifts into the social work practices or remains in the local authorities it will be there," she said.
Responding, Lord Adonis, the schools minister, played down the significance of the potential pilots which could last between two to five years, describing them as a "minnow" compared to the "whale" of local authority social services.
Trials of looked-after children
There are around 60,000 children in care at any one time and 28 per cent on average have special educational needs, against a national average of 3 per cent. They are five times more likely to move schools at key stage 4 and eight times more likely to be excluded than other children. A quarter of adults in prison have spent time in the care system.