They already spend 10 long months studying and being judged by their academic ability. By the time summer begins, they are tired of working their brains. If they are forced to continue school, they may not try as hard, maybe not even at all. Pupils also need time with their friends, to play and relax, and also with their family, building relationships and learning from their guardians. School during summer may help out working parents, but that isn't the government's responsibility.
Responsibility belongs to parents.
Whether Davis and other policy-makers realize it or not, children learn even while they are at home. Just because they are not learning vocabulary and mathematics doesn't mean they aren't learning something valuable that is necessary for their future. Being home with the family gives parents a chance to teach their children home economics, to take their children fishing or to teach them how to ride a bike. Many also blame high crime rates on the summer months. Because kids are not in school, they use their free time to do harmful things.