"There is a limit to how much kids can benefit from home study," Cooper says.
He agrees with an oft-cited rule of thumb that students should do no more than 10 minutes a night per grade level — from about 10 minutes in first grade up to a maximum of about two hours in high school.
Yet other evidence suggests that some kids might be taking home much more work than they can handle.
Robert Pressman, Ph D, and colleagues recently investigated the 10-minute rule among more than 1,100 students, and found that elementary-school kids were receiving up to three times as much homework as recommended.
In fact, too much homework can do more harm than good.
Researchers have cited drawbacks, including boredom and burnout toward academic material, less time for family and extracurricular activities, lack of sleep and increased stress.
"I think there's a focus on assigning homework because [teachers] think it has these positive outcomes for study skills and habits.
But we don't know for sure that's the case." Even when homework is helpful, there can be too much of a good thing.
Both the National Education Association and National Parent Teacher Association support that limit.
Beyond that point, kids don't absorb much useful information, Cooper says.