The most critical question about homework is “How much homework should students do?” Experts agree that the amount of homework should depend on the age and skills of the student. Many national groups of teachers and parents, including the National Parent Teacher Association (PTA), suggest that homework for children in kindergarten through second grade is most effective when it does not exceed 10-20 minutes each day. In third through sixth grade, children can benefit from 30-60 minutes of homework per day. Junior high and high school students can benefit from more time on homework, and the amount may vary from night to night.
Reading at home is especially important for young children. High-interest reading assignments might push the time on homework a bit beyond the minutes suggested above.
These recommendations are consistent with the conclusions reached by many studies on the effectiveness of homework. For young children, research shows that shorter and more frequent assignments may be more effective than longer but fewer assignments. This is because young children have short spans of attention and need to feel they have successfully completed a task.
http://www.ed.gov/parents/academic/involve/homework/part.html
