I don't have an answer to the pros or cons, but I know my daughter's Montessori Charter school is contemplating the year round program as well. We are the Western Edge of WI. Wouldn't go into effect until the 2016-17 year when she will in theory be in the adolescent program in a different building. Our school district does have 1 school on the year-round program and it is now in it's 2nd year. The positive of the year round program is that they get 2 week breaks through out the school year instead of one big chunk off in the middle. They have the year round school set up with morning enrichment activities on the off week (except when the rest of the district is out) which helps for those who need to deal with child care issues. I'm not opposed to it if the school is air conditioned so summer classes are not miserably hot. My daughters school is in a brand new building, so that should not be an issue.