Just look at summer programs... some great research out there showing that low SES and high SES students make similar gains throughout the school year which are then lost over the summer by the low SES groups. We aren't really agrarian anymore. Year round school takes serious money, but can work and be a positive benefit for two income households in addition to learning outcomes.
If a longer school year causes students to forget less over summer break, there should be less need for review in the fall, and teachers should be able to cover more new material in the school year. I would support a shorter summer break if paired with a system that shortens K-12 by one year -- after 11th grade students would go to college, trade school, or work. I would not support merely extending the school year without increasing academic standards in some way.
