By Angela Harrison BBC News Online education staff in Bournemouth

Teachers are warning families they could face chaos if different councils continue pressing ahead with their own plans to change the school year.

The spring break would be fixed - not necessarily at Easter

Delegates at the annual conference of the NASUWT teaching union called for a nationally-agreed school year.

About 18 local authorities have decided in principle to adopt a new pattern, known as the six-term year.

This involves a shorter summer holiday with a few extra days added on to what are now half-term breaks.

Many councils have been asking local people for their views.

Package holidays

The NASUWT said a piecemeal approach would lead to problems for many teachers and families.

Parents who had children at school in different areas could find their children were on holiday at different times, delegates warned.

And theories that the changes could mean cheaper package holidays were "daft", they said.

Some delegates said teachers should be allowed to keep the main perk of their job: the long summer break.

Jane Derbyshire said any changes should be across the country.

"There should be a national holiday pattern, at least then we will all know when we are on holiday," she said.

Joy Windsor said Hampshire - which has been canvassing opinion on the issue - wanted to make the change unilaterally.

"The issue must be debated at national level not on an ad hoc basis," she said.

Creeping in

Graham Jackson said the issue was creeping up on his area, Berkshire.

"The issue is creeping up from Hampshire. Many students cross boundaries to go to school, as do staff," he said.

"Having different patterns in Berkshire and Hampshire would be total madness."

Eamonn O'Kane, the general secretary of the NASUWT, said the arguments for changing the school year seemed to be "much pain for little gain".

"NASUWT members have expressed many valid concerns over different term-time patterns in neighbouring LEAs.

"Some teachers have children at school in different LEAs to the ones in which they work, meaning they must pay childcare costs if they are teaching while their children are on holiday.

"LEAs which insist on pursuing alternations may find tinkering with the school year causes further problems with recruitment and retention of staff."

The conference passed a resolution deploring the decision by some education authorities to push ahead with the changes in the school year despite the opposition of those representing classroom teachers.