Schools in England and Wales have been told to overhaul their staffing structures by the end of the year.
Teaching and learning is the new focus of extra payments
In some cases it will mean teachers will lose money, as "management allowances" are scrapped.
Instead extra payments will focus on teaching roles, but staff may have to compete with colleagues for these - and are not guaranteed to get the money.
The changes have been agreed between the government and some, but not all, of the education unions.
Head teachers have to come up with a new structure over the summer. School governors are supposed to agree changes in the late autumn.
"The deadline of 31 December is very tight," said the general secretary of the Secondary Heads' Association, John Dunford.
"But it should be possible for schools to meet this deadline with the guidance having appeared at the end of May and the outline of the scheme having been apparent since about February."
That was when the independent School Teachers' Review Body, which makes recommendations to ministers on pay and conditions in England and Wales, proposed the changes.
The current five management allowances range from £1,638 to £10,572.
A study commissioned by the review body found little consistency in how these operated.
They were often paid for administrative rather than management responsibilities, and sometimes were used to recruit or retain teachers, it said.
The new payments for additional responsibilities - TLRs, in the jargon - are payable at two levels ranging from £2,250 to £5,500 and from £6,500 to £11,000.
Dr Dunford said: "I think heads regard it as a welcome opportunity to review their staffing structures and to focus extra payments on teaching and learning responsibilities."
It also meant they could recognise the role of support staff, who now do many of the administrative tasks for which teachers might have had extra payments.
He said there was now greater flexibility in the system for separate payments to recruit and retain teachers.
At the National Association of Head Teachers, which represents most primary school heads, general secretary David Hart has written to Education Secretary Ruth Kelly to say the timescale is "impossibly tight".
He told her: "Head teachers need longer to consult and create structures which will have credibility and longevity."
"Considerable resentment" was building up, and local education authorities were ill-informed and unable to support schools.
But he is not hopeful of a change.
"I suspect the secretary of state has crossed the Rubicon and I don't think she wants to go back," he told the BBC News website.
A spokeswoman for her department said it believed the changes were "fair for teachers and reasonable for schools".
Mr Hart said that, at a local level, representatives of classroom unions had been threatening industrial action if members currently getting management allowances did not have these transferred onto the new structure.
Official guidance says "this is emphatically not an assimilation exercise" - teachers getting management allowances cannot necessarily move to an equivalent post with the extra pay that goes with it.
Head teachers and governors have to decide what roles they need then who should fill them.
Where a post is largely unchanged, the existing member of staff "should be 'slotted in' to the post".
But if there is to be a new post, normal recruitment procedures have to be followed.
And where a post combines a number of existing responsibilities, the staff involved should have to compete for it.
And just because someone meets the criteria for an extra payment does not mean they will get it.
The changes are to take effect within three years.
During that time, a "safeguarding" process means people's salaries will not suddenly drop even if they lose allowances.
But the National Union of Teachers, which opposes the changes, says they may lead to pay cuts for thousands of teachers.