How much homework is too much?

A recent study of 7,451 teenagers in Spain examined the correlation between time spent on homework and academic achievement in math and science. Results showed that homework done by the student independently for 60-70 minutes a day yielded the best results.

Subjects had a mean age of 13.78. They were given a questionnaire asking about frequency and duration of homework by subject, and if they did homework independently or with parental help. Academic achievement was determined using math and science standardized test scores adjusted for gender and socioeconomic status.

Results showed that students' math and science scores increased when:
Homework was assigned on a schedule

Students did their homework independently

Students were assigned 60-70 minutes of total homework. More than 90 minutes of homework a night had a detrimental effect on students' test scores.
The authors noted that students who did 70 minutes of homework with parental help scored lower than students who did 70 minutes of homework independently. They concluded that how the homework was done was more important than amount of time spent doing it, citing the possible explanation that self-regulated learning is related to higher academic achievement.