In the December 2008 Phi Delta Kappan, Larry Cuban offers an interesting analysis of the efforts to lengthen or alter the school day and year. He goes through the history of reform efforts. He even dispels the myth that our long summer break is a remnant of an agrarian economy; it is actually a result of middle-class parents wanting time to go on vacation or send kids to camp.
One of the major problems is the assumption that schools are just designed to prepare workers:
"By blaming schools, contemporary civic and business elites have reduced the multiple goals Americans expect of their public schools to a single one: prepare youths to work in a globally competitive economy. This has been a mistake because Americans historically have expected more from their public schools."
Cuban points out that there are many reasons that citizens support public education, including preparing responsible citizens, promoting common cultural values, dispel societal inequities, etc. So, building an entire reform effort around the needs of the business community does not actually work.
Instead, Cuban recommends improving the quality and focus on "academic learning time," "improving the quality of the time that teachers and students spend with one another in and out of classrooms":
"If policy makers could open their ears and eyes to student and teacher perceptions of time, they would learn that the secular Holy Grail is decreasing interruption of instruction, encouraging richer intellectual and personal connections between teachers and students, and increasing classroom time for ambitious teaching and active, engaged learning."
My only addition to Cuban's recommendation is that we should consider that not all learning time happens in a classroom in the presence of a teacher. There is a reason that middle-class parents demanded camp opportunities, and a reason that kids who go to camp don't fall as far behind academically as those who do not. It is not because those camps are focused on academic learning with classroom teachers. It is because high quality, focused learning time is more effective if it is balanced by a culture of out-of-school learning experiences.