"[T]here is no overall positive correlation between homework and achievement (by any measure) for students before middle school or, in many cases, before high school" (The Homework Myth, p.38).
"[Harris Cooper] mentioned another large study he had come across. It, too, found minuscule correlations between the amount of homework done by sixth graders, on the one hand, and their grades and test scores, on the other. For third graders, the correlations were negative: more homework was associated with lower achievement" (The Homework Myth, p.39).
"But it's worth pointing out separately that no evidence exists to support the practice of assigning homework to elementary students. No wonder 'many Japanese elementary schools in the late 1990s issued 'no homework' policies'" (The Homework Myth, p.40).
"Consider the results of the 2000 [NAEP] math exam. Fourth graders who did no homework got roughly the same score as those who did thirty minutes a night. Remarkably, the scores then declined for those who did forty-five minutes, then declined again for those who did an hour or more!" (The Homework Myth, p.41).
"In a separate analysis of the 1999 TIMSS results that looked at twenty-seven U.S. states or districts as well as thirty-seven other countries, meanwhile, 'there was little relationship between the amount of homework assigned and students' performance'" (The Homework Myth, p.43).
For now, I'm going to stop. As I read, I'll add more, and, eventually, I'll comment.