Every person is a little different. One of our kids is definitely very alert and ready to learn in the early morning. The other one, unfortunately, isn't. The one-size-fits-all schedule is much more for the convenience of adults than for the effectiveness of education, unfortunately. Some of the other commenters point out that important things should not be too early or late. That may well work better. But I'd be a little worried that there is no such thing as one good schedule that works for every child or even a significant fraction of children.