The reason for that is that in a family where a child is at a year-round school and his or her sibling is at a normal school, they may have separate vacations. Then the parents may have to get one kid ready for school and prepare activities for the other child, who is at home. This also makes it very difficult to plan family vacations. Another criticism I've heard is that students and teachers can burn out without the long summer break, although proponents of the program say that burnout is less likely at year-round schools, because the breaks are more evenly distributed. Well, it depends on whom you ask.
Some teachers love it.
They say the frequent breaks give them and their students a chance to refresh. Teachers at the multi-track schools tend to be more critical. That's because some of them actually have to switch classrooms every few weeks in order to accommodate the various tracks. Other teachers say they've tried the program and didn't actually see any academic benefit. That's certainly one of the strongest arguments of those who oppose year-round education.