As a teacher and a mom I have pretty strong thoughts about this whole issue. I will try to summarize them briefly.
I don't think that extending the school year is what is needed, but rather moving the schedule around so that we had a week's break after each 9 weeks of school to allow everyone (kids and teachers) a breather. (This is especially needed if you are teaching higher level indepth courses.) And then a month at Christmas and around a month for summer. This would eliminate the need for extended review, but would allow the much needed breaks for all involved.
If you are not in the classroom with kids all day everyday (whether it be 18 elementary kids all day long or 150 middle/high schoolers in various classes cycling through) dealing with not only their academic needs, but their social and developmental needs, as well as dealing with their parents/guardians/family members/parole officers/students' kids etc. trying to actually teach the kids what they need - not just to pass some state mandated test, but to have them actually
learn something you have no idea how utterly exhausting it is. The idea of adding on hours to a school day, or more days to the year makes me shake my head and want to resign now.
At the moment it is the end of the first marking term - we are all tired and need a break, but we don't get one until November - Thanksgiving weekend. We will muster through, because we have no choice, but PLEASE keep in mind that as a teacher (if your good and care) you are often taking home 3-4 hours of work EVERY NIGHT! of marking or planning or report writing because 1 50 minute period a day is not enough time to even think straight, forget about doing all the stuff you need to. I have almost 20 years teaching experience, and I know what I am doing and I still do close to 3 hours of work a night just to stay a day ahead of requirements.
Not to mention of course that with a master's degree in physics and all of these years experience, I do all of this for less than $50,000 a year.
So, while I understand the need in our society for parents to have a place for their kids to be while they work, and I know our country's education is not where it should be right now, rather than simply extending the school year give us power back in the classroom to teach the kids in ways that we know will be beneficial to our students, rather than requiring us to spend all of our time prepping them for tests.
As far as our specific population of kids - I would not want my DD to spend any more time in school than she does now. She needs free play time at home with the family, or at the beach or on vacation. I agree with other posters that in this country the idea of extra time during the day to allow for a longer lunch and PE everyday sounds great, it would probably be the first thing to be cut and they'd end up in more test prep classes rather than getting what they need.
