Six-term benefits in doubt
A report, for the Local Government Association, which has spent the past five years campaigning for councils to adopt the new calendar, found little evidence to support the changes.
The National Association of Schoolmasters Union of Women Teachers, which is involved in disputes in eight areas where the changes resulted in shorter summer holidays, said the publication of the report was astonishing.
Chris Keates, acting general secretary, said: "This is a classic example of putting the cart before the horse. The LGA has gone for the changes and then commissioned the research to see if it has any value."
Thirteen councils changed their academic calendar this year and a further 32 have agreed in principle to do so. Ms Keates said the switch had created disruption in some authorities.
The literature review by the National Foundation for Educational Research looked at evidence from the United States and Canada which showed that their alternative calendars had no significant effect on attainment.
It concluded that changing to a similar arrangement in Britain would not have any impact on pupil achievement, attendance, motivation or exclusion.
The study said the issue had not been "explicitly researched" and the authors suggested there was a need for empirical research which distanced itself from "advocacy and assumptions".
An LGA commission recommended councils introduce six terms of roughly equal length, arguing that predictable and standard dates would make it easier to plan the curriculum and provide a more balanced school year.
In March, 45 councils agreed in principle to introduce a standard school year, with 13 implementing it this year.
Fleur Young, the LGA's standard school year project leader, said: "The evidence isn't out there because nobody has sat down to do it systematically. We weren't surprised when the results came back."
She said a second round of research would evaluate the experience of the standard calendar in the 13 councils which adopted it this year. "If you have equal length blocks of time it just has to be much better to plan and deliver the curriculum," she said.
The standard school year was adopted this year by Bath and North East Somerset, Bristol city, Essex, Gloucestershire, Isle of Wight, Lincolnshire, North East Lincolnshire, North Somerset, Oxfordshire, Somerset, South Gloucestershire, Swindon, Wiltshire.
Review of the evidence relating to the introduction of a standard school year, Anna Eamer, Caroline Sharp and Paula Benefield. www.nfer.ac.uk
LGA proposal for school year 20045
Trainingplanning day August 31
Term one September 1 to October 20
Term two November 1 to December 21
Trainingplanning day January 4
Term three January 5 to February 11
Term four February 21 to April 1
Term five April 18 to May 27
Term six June 6 to July 19