Government attempts to reform the school workforce were thrown into further jeopardy this week as the country's biggest union for support staff failed to reach agreement.
Unison suspended its involvement in June following a vote by delegates at the union's annual conference.
Activists said they wanted the agreement renegotiated to include national pay and career structures for support staff. The union's leadership set a September deadline to iron out the problems with ministers.
Headteachers said that the next stage of the agreement, including limits on the time teachers can spend covering for absent colleagues and guaranteed non-contact time would be endangered in some schools if Unison pulled out.
This week the union confirmed it had failed to arrive at a solution with the Government or local-authority employers over new national guidelines.
Its 40-member executive was due to vote yesterday to either suspend its involvement in the deal or seek further talks with individual regional branches over a national deal.
Either way the delay will further frustrate the Government's attempts to have the workforce agreement fully implemented by September 2005.
The union, which represents 250,000 school support staff, says it has been forced to seek a national settlement because of the slow progress towards better pay and conditions for school staff at a local level. The TES has learned that agreements have been reached with just 35 out of 150 local education authorities. These would cover moves to full-year (rather than term-only) contracts and pay increases for new responsibilities.
Negotiations have not started in almost 60 authorities, more than a year after the agreement was first implemented.
Unison's leadership has also been angered by the Government's five-year education strategy, smoothing the way for all secondary schools to win foundation status. This allows schools to act as individual employers and the union fears that negotiations over new contracts will be complicated further.
Christina McAnea, Unison's head of education, said: "The atmosphere of talks over the summer has been positive but we are still looking for support from the Government to reach a national framework the local authority employers will agree to."
The local government Employers' Organisation insisted deals could still be brokered locally by 2007.
Mike Walker, employers' secretary, blamed the pressures on council budgets and failure by local union branches to co-operate. The Department for Education and Skills refused to comment on Unison's involvement.
Failure to finalise details of the deal are already having an effect, it was claimed this week.
Select Education, the support staff recruitment consultancy, said it had been contacted by hundreds of schools unable to implement the latest terms of the agreement.
John Dunn, marketing director, said: "It's clear from our discussions with schools that many teachers are still carrying out certain tasks, even though contracts may no longer require them to.
"Many teachers will have spent several days before term starts getting their classrooms ready."