"Public Education" has not evolved logically. We are still stuck with an omnibus "See You in September" paradigm based on summers off to help the family with the harvest. Honestly, does everyone understand that this is the historical "logic" behind the US Public Education Calendar?
Assuming that increased student success is the desired outcome, there is absolutely NO reasonable and logical purpose to having EACH AND EVERY student REQUIRED to PHYSICALLY attend via CLASSROOM SEAT TIME through the hottest months of the year. 
Students in need of additional help should be required to attend year-'round school 52 weeks per year with no breaks until they become satisfactory.
Students who make satisfactory progress should be enrolled in courses September to June, with July and August for vacation because those are the hottest months.
Students who are exceptional should be allowed to attend half time for the "Three Rs" and be otherwise freed up to seek their gifts in music, art, STEM, etc.