The main reason behind this idea is to raise teacher salaries. In fact there is no evidence to support the idea that longer school days and longer school years are helpful for most students.
We have a friend who is a teacher in the Dallas ISD. She teaches 2nd grade. They consolidated two classes, and put them together in her one room. Took away the teacher’s aid. Took away all support, and gave her several developmentally challenged, and several purely retarded students. She’s already pretty much given up on really teaching. It’s turned into a baby-sitting class, with less than 15 minutes per student, probably less than 10 per student since so much time has to be spend on these “special needs” students. The smart ones will be bored, the ones who can achieve but need help won’t since they won’t get the time they need, and the “special needs” students won’t advance at all since she just doesn’t have the resources and assistance needed to work with these children.
It’s not more days in the classrooms. It’s providing a learning environment that actually works.