Union stands firm over shorter summer holiday
Teachers have said they will resist any attempt to shorten the six-week school summer holiday.
The National Union of Teachers (NUT) said any move to cut the traditional summer break would harm children's learning and teachers' wellbeing.
The union passed a resolution at its annual conference in Torquay.
It comes after NUT members in Nottingham staged a one-day walkout over proposals by the city council to introduce a five-term school year.
The move, which could be implemented in 2013, would see the summer holiday cut from six to four weeks.
Nottingham City Council says the move will boost attainment and attendance.
The council says having shorter breaks means pupils are more likely to remember what they have learnt.
But NUT members are planning to stage two further one-day strikes later this month.
Nottingham teacher Tom Unterrainer told delegates at the NUT annual conference: "We've looked for rigorous academic research which points to the fact that learning loss takes place. There is none.
"But there's plenty of evidence, plenty of empirical evidence, real world evidence out there, around the world, to show that school holiday length and the lengths of teachers' holidays and the length of time that students and young people are out of school has no verifiable impact on their outcomes. It's a nonsense."
Speaking during the debate, Sheena Wheatley said: "A five-term year represents a major attack on our conditions of service."
"I don't think I need to describe the impact of shortening the summer break, not just for us and our families, but also for the young people that we work with.
"The projected eight-week terms would have a major effect on our workload and ultimately our health, I believe."
Fellow Nottingham teacher John Illingworth said that if the plans went ahead, the city would have "the shortest school summer break in the world, at just over four weeks".
Mr Illingworth said: "We don't want Nottingham to become a laboratory for testing how far we can drive our young people."
A six-week break was important for children and teachers, Mr Illingworth said.
"This union has stood up over the years for the right for children to play. There's been an attack on play in our schools and we're attacking children's right to play outside school."
A Department for Education spokesman said: "It's rightly down to schools and local authorities to decide their own term dates and holidays, not government.
"In doing so, term times must be in the best interests of pupils."
The call to resist changes to the school holidays was part of a wider motion at the NUT conference on teacher workload which claimed the amount of work teachers face was getting worse.
It called for the union to campaign against the problem, including national ballots for strike and non-strike action.