nothing
Lessons learned remain fresh when there are no lengthy breaks. Schooling is completed quicker allowing students to move on to higher education or work at a faster rate.
Shorter, more spread...
They do not boost education, in fact, some school found a decline in test scores after trying year-round schools. They also dont have any more days than a traditional 9 month school. They often have...
You don't get the "brain drain" during the summer. Imagine having 3 weeks of skiing time. People think year round schooling is just more school, but it's still the same 180 days of school.