Great point, Ev.
Younger children can do only an hour a two a day. Then as they get older, move up to 3 and then 4 hours (and as they get older, more of it can be self-taught study, too).
The law only required us to do 4 hours a day, I'm not sure about other places.
When I go to college and saw how some of the people were dumb as rocks, I was wondering, "What DID you do all those hours/years in public school?"
In summary, the idea of teaching your child ALL DAY LONG is not necessarily an accurate picture.