The biggest teachers' union is still refusing to sign a deal on reducing workload, with less than a day left before the government's deadline.

While other teachers' and head teachers' unions are set to accept the workload arrangements, the National Union of Teachers says it has no plans for a last-minute change of heart.

The biggest sticking point for the NUT is the proposal that classroom assistants could be in charge of a class or could provide cover for absent teachers.

The deal negotiated with the government is designed to reduce teachers' workload and to provide more time for marking and lesson preparation.

And to free up teachers' time, the government is proposing that thousands of classroom assistants should be recruited.

Classroom managers

Teachers would take on a more managerial role and would no longer be expected to carry out administrative and non-teaching tasks.

But the NUT wants stricter guidelines on how classroom assistants can be deployed and limits on the ratio between teachers and assistants in schools.

Other teachers' unions have accepted the deal, which will be formally adopted on Wednesday, the deadline set by the government.

Last week, the School Standards Minister David Miliband urged teachers to seize this "once in a generation" opportunity to modernise the teaching profession.

But the NUT says that it is willing to stand alone against the proposed changes to teachers' contracts.

A spokesperson said that even if the deadline was not met, there was no immediate prospect of confrontation, and that further consultation was anticipated.

The union says that it has written to the government expressing its concerns over the workload arrangements - and has so far not received a reply.

And it rejects the negotiating deadline as "artificial" and an attempt to apply pressure by the government.