His research suggests that homework in the elementary grades has little correlation to achievement. His research regarding the value of homework in the higher grades is a mixed bag. Cooper seems to have identified a sweet spot of homework, at least in terms of quantity. Some homework, he concludes, is associated with improved scores on standardized tests, but excessive amounts of homework—more than 60 to 90 minutes in middle school, and more than 2 hours in high school—is actually associated with lower standardized test scores. Essentially, Cooper’s research affirms the NEA’s 10-minute guidelines.