Teachers are entitled to take time out for marking and preparation

The Association of Headteachers in Scotland said guidelines, which allowed teachers time out to do marking, put too much pressure on senior staff.

Under the landmark McCrone deal, teachers must get one-and-a-half hours away from the class during the 25-hour working school week.

The provision will rise to two-and-a-half hours from August 2006.

Employers said "mature" discussions were needed to help deliver the scheme.

The provision for non-class time was among the key recommendations of the McCrone report, which lays out the blueprint for teaching in Scotland in the 21st century.

'Teacher shortage'

Gordon Smith, president of the Association of Headteachers in Scotland, said McCrone had resulted in the need for more teachers.

He said: "For a long time now depute heads and head teachers have been the finger in the dyke for many of the problems from the recent teaching arrangements.

The increase in preparation and marking time is a good thing and we intend to deliver it Ewan Aitken Cosla

"When it comes to teachers in front of classes we need more of them, and perhaps children will have to be sent home before this message gets across."

Speaking on behalf of Cosla (Convention of Scottish Local Authorities), Councillor Ewan Aitken said it was "entirely unhelpful" to suggest children would be sent home.

"The increase in preparation and marking time is a good thing and we intend to deliver it," he said.

"But the negotiations that are required to deliver it must start from a mature conversation and not threats from afar."