your example doesn't contradict the idea of having a longer school day or school year. as others have said, kids who lack a nurturing home environment can benefit from a nurturing environment at school (if that's what it truly is).

for example, school could open at 6am for parents who work early, but not start until 9am. the intermediary time could be nap time, unstuctured play, or guided exploration (gardening, science experiments, even animal husbandry in rural areas). between structured classroom time, they could have more breaks for more naps, play or exploration. school could end later so parents can pick them up after work, and have shorter and more frequent vacations so kids don't forget so much in-between.

you could even have morning or evening joint learning times, where parents join in to learn how to teach and encourage their kids (such programs seem to help break the cycle of poverty).