The BBC report about Norwegian research on the impact of hay fever on exam results http://www.bbc.co.uk/news/education-34062879 added a small (but for some important) addition to the reasons why we should reconsider the structure of the school year. I would propose the following:
Begin each school year in January
Have holidays at Easter (2 weeks), June and July (7 weeks), October (2 weeks), Xmas (2 weeks)
The rationale is that the urgency of getting in the harvest should no longer drive the structure of education. Having the summer break in August is usually a disappointment because having sat in classrooms through the heat of June and July, children (and families) either get wet in August in the UK or go abroad for the sun in Spain etc.
Secondary exams (and primary SATs) could be sat in November just before Christmas sets in.