My kids (4th and 7th) attend a school with a year-round schedule, and we (kids and parents) love it:
* They are less stressed because there is more breaks throughout the year. Teachers seem less stressed, too, because they don't have to pack so much in.
* They retain more in the summer.
* Outside of academics: it's really nice to have the option to take longer vacations outside of spring break and summer break.
I'd love to see more schools move to it... 3 months off in summer seems very antiquated in hindsight.