By Justin Parkinson BBC News Online at the NUT conference in Harrogate

The National Union of Teachers, holding its annual conference at Harrogate, is considering setting a unilateral limit on class sizes - with the threat of sending children home if there are more than 27 pupils.

HAVE YOUR SAY It's just teaching on the cheap Richard, UK Send us your comments

The union conference is to vote on Tuesday on how it will pursue a campaign against a national agreement on reducing workload.

The workload deal, struck between the government and other teachers' unions, will allow classroom assistants a much wider role in schools.

And the NUT is strongly opposed to suggestions that "higher level" assistants could take classes unaccompanied.

The workload deal, signed in January, would allow tens of thousands of classroom assistants to take on administrative and support tasks, allowing teachers time for lesson preparation.

But the use of assistants to work unaccompanied will undermine the professionalism of teaching and offer a cut-price route to tackling teacher shortages, says the union.

Refusal

Bill Greenshields, a member of the NUT's national executive, told the conference: "There will be a two-tier staffing situation.

"It's going to be the kids who are already suffering from disadvantages who will be forced to accept teaching by assistants.

It's not fair on the teaching assistants Teacher Alison Long More comments

"We need to set a bottom line for the government - a qualified teacher for every class and no doubling up by unqualified staff."

But the amendment supported by the conference, which proposed refusing to teach over-size classes to highlight the scale of staff shortages, was described as "unfortunate" by the NUT's general secretary, Doug McAvoy.

But Mr McAvoy repeated the union's opposition to the use of classrooom assistants to cover for absent teachers - with the leadership proposing that teachers should refuse to carry out any task which would allow assistants to take a class alone.

"What the government wants to introduce would lower the professional status of teachers," said Mr McAvoy.

The NUT executive is calling for action against the agreement on a local level.

However, Mary Compton, the vice-president, disagreed, saying: "Not all teachers are strong enough to go it alone.

"What we need is national action, which will be popular and effective."

The NUT claims the agreement will not remove the "excessive" workload of teachers, as it does not offer any "guarantee" of marking and lesson preparation time or limits to teaching hours.