Cooper (1994) discovered the presence of a strong grade-level effect when assessing homework’s
effect on academic achievement as defined by school grades. High school students, 14-16 years of
age, who were assigned homework performed 69% better than students in a class without assigned
homework. For students in junior high school, 11-13 years of age, the average homework effect was
only half this size. Finally, in elementary school, homework appeared to have no effect on achievement.