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That recommended level goes by the 10-minute rule, or 10 minutes for every grade level starting with first grade. For example, a first-grader should have about 10 minutes of homework a night, all subjects combined. A sixth-grader should have 60 minutes, while a high school senior should have no more than two hours of after school assignments, according to the National PTA's website.

But according to the study, parents responded that their children are doing much more. On average, first graders had 28 minutes of assignments at night, while kindergartners, who are not recommended to have homework, according to the standards, had 25 minutes a night finishing assignments, more than what is recommended for a second-grade student, CNN reported.

Some experts say that too much homework is taking a toll on students' health. A study from the Journal of Experimental Education found the work is causing migraines, ulcers, and sleep deprivation.