The Education Secretary, Ruth Kelly, has qualified a proposal that all secondary schools in England should take a share of disruptive pupils.
Ruth Kelly said she was "building on what's gone before"
She said the principle would apply only after local partnerships had been formed and had agreed specialist provision to cope with such children.
And she is giving schools an extra year to begin that process.
Her predecessor, Charles Clarke, had wanted every head teacher to have arrangements in place by September.
Ms Kelly said in a radio interview that she was announcing that this admissions policy "need not apply to excluded pupils until schools are confident that they have got the necessary facilities in place to deal with these pupils".
Asked whether this was a response to criticism of Mr Clarke's plan, she said: "I think the proposal is right that schools should have responsibility for these pupils but I also think that schools are in different places and have different facilities available.
"They don't necessarily already have the facilities to deal with disruptive pupils.
"So I'm absolutely making it clear that schools should have the tools they think they need to deal with disruptive pupils before they have to deal with them," she told BBC Radio 4's Today programme.
She told head teachers in a speech on Tuesday: "I am giving this additional breathing space on the clear expectation that all secondary schools should be part of such agreements by September 2007," she said - but would legislate if necessary.
She said: "excluded pupils cannot be left on the scrap heap".
"By exercising their collective buying power, I expect that groups of schools will be able to use customer pressure to drive up the quality of provision outside schools for challenging pupils, which for too long has been the Cinderella of the education world," she said.
Her move is part of what she is calling a "zero tolerance" approach to even low-level school indiscipline.
The general secretary of the Secondary Heads Association, John Dunford, said: "Schools are prepared to work collaboratively in dealing with difficult pupils, provided that the government and local authorities delegate adequate funding to do the job properly."
And he did not see how another proposal - which he characterised as "the threat of repeat Ofsted visits" - fitted with the new inspection framework, currently going through Parliament.
"Where inspectors find discipline problems, the emphasis should be on the support that she mentions, not on more inspection," he said.
The Shadow Education Secretary Tim Collins, said Ms Kelly's announcement was "a breathtakingly cynical ploy".
"Ministers will still force schools to take disruptive pupils - guaranteeing a thug in every playground - but shamelessly hope to get some credit by postponing this daft and dangerous idea until September 2007."
The Tories have been reminding people of their own five-point plan on discipline:
- scrap independent appeals panels
- give heads the right to require that enforceable home-school contracts are a condition of attendance at their schools
- scrap the idea of schools being forced to take a share of disruptive pupils
- give teachers a guarantee of anonymity until a criminal charge is brought if accused of abuse
- fund more schools for expelled pupils and expand CCTV, random drug-testing and metal detectors.
The Liberal Democrats say the other parties are missing the point by tackling bad behaviour after the event - what is needed is a curriculum that engages all pupils.