I'll post this without any real citation, except the word of a high-school, then college teacher and neuroscientist i have known.

That teacher said: classes are not for real learning, but for getting the first contact, or solving doubts. Homework is where the magic happens. Small amount of (handwritten) homework, related to the same day class, and a good sleeping night.

He also advocated for less class time, some school time for homework, and more time of extra activities not related to TV watching or internet procrastination. Also, reading, reading and more reading.