An extra hour of homework costs more than it earns if it comes out of sleep

"He'll finish his homework, then go to bed." The logic looks solid: less sleep, more study time, better grades.

It breaks at the first step. Sleep loss hits exactly the things school runs on - memory, attention, emotional control, motivation - and consolidating the day's learning is something the brain does during sleep. A rested child who studied less outperforms a tired child who studied more.

Nine to eleven hours at school age. Sleep is not time taken away from learning; it is the part where learning is stored.