It's worth noting that research is being done on the usefulness of homework and, with the appropriate caveat that this is a newspaper article and not the actual research, here's a brief summary.
There's little evidence to show that homework is effective among primary-school-aged children – except for those who are performing below their peers.The question is, do politicians who impose "mandatory homework" policies on the early grades care if it actually helps, or do they want to diminish kids' home lives for the sake of looking like they're "doing something", even if it's not productive and potentially counter-productive?
Many homework experts live by the “10-minute rule”: Kids shouldn't do more than 10 minutes of homework for each grade they're in. That means a student in Grade 1 would do no more than 10 minutes, while a student in Grade 4 would do no more than 40 minutes. High-school students could do up to two hours a night. Spending more than two hours is not associated with higher academic achievement, concluded a 2006 Duke University study led by Harris Cooper, a homework expert and professor in the department of psychology and neuroscience.
Homework should reinforce what a child has already learned, be presented in a clear, manageable way and be engaging.