Caroline Sharp, of the National Foundation for Educational Research, says her assessment of "year-round" schools and summer learning loss suggests that changing the academic year will have little or no impact on standards.
Multi-tracking, where cohorts of students have different timetables and holidays to maximise the use of school buildings, could be a useful aternative to building new classrooms at crowded schools.
But given the marginal effect on standards, any changes to the school year need to be balanced against the disadvantages of being out of step with other schools, the effect on family, work and childcare, and the timing of exams.
Miss Sharp will be presenting her findings at an Association of Teachers and Lecturers' conference tomorrow. She looked at research in the US and UK on summer learning loss, and on performance at "year-round" schools.