A Prince George’s County reader who identifies herself on my Web page as JenPam2003 did not like my suggestion that parents enforce a reasonable amount of time for their children’s homework. I said their kids should do something else when that time expired, even if the assignments are not finished.

Her daughter, a junior in the demanding science and technology program at Eleanor Roosevelt High School, has between three hours and four hours of homework each night. “If a student leaves work undone, she is left unprepared for the next day,” she said. “Further, she is penalized by the teacher and her grade takes a hit.”

The kind of passive resistance I was proposing, inspired by a new book “The Learning Habit,” would be messy in high school, as JenPam2003 correctly pointed out. But what about younger grades? The book’s authors, Stephanie Donaldson-Pressman, Rebecca Jackson and Robert M. Pressman, say 10 minutes of homework a day based on grade level — 20 minutes in second grade and 80 minutes in eighth grade — would work.

The little-known truth at the heart of their suggestion is this: We know from decades of research that the amount of homework our children do in elementary school has no effect on how much they learn. Competent teachers can get their messages across during class. Homework in that age group does little more than make parents feel better about the school.

I didn’t know that when I was an elementary school parent. I would have objected if my children’s teachers didn’t assign homework. The parents at my eldest grandchild’s school feel the same way. He is in kindergarten. To finesse complaints, his teacher announced on back to school night that kindergarten teachers were not allowed to give homework by order of the school board.

Fifty minutes of homework a night for fifth graders seems about right to me — not too much to spoil the evening and not too little to freak out the parents. But what will elementary school teachers who give more than that do if they hear parents are countermanding their orders?

“My fifth grader just spent three-plus hours on her homework, which included math, writing and social studies,” said a reader who signs on as CalvinTheDog. “A majority of the class did not finish and were told that they would have to stay inside during recess to work on it.”

“If a teacher is assigning too much homework, the parents should be talking to the teacher, to other parents, and eventually to the principal,” said a frequent commenter who signs on as LaborLawyer. He is correct, and I cannot think of a better way to make such conversations meaningful than sending an e-mail to the teacher and the principal explaining your family’s homework rules. You don’t need to e-mail other parents; such news will spread.

One reader, signing on as Reythia, said teachers shouldn’t be blamed if a student spends a long time on math homework because he doesn’t get the concept. Really? Good teachers check for understanding regularly, and they look for ways to help students who don’t get it. They would want to know that their homework assignment took longer than it should have.

Since grades are unlikely to matter much in elementary school, parents there have some maneuvering room. High school is different. There are more consequences for failing to complete work. But maybe we exaggerate the problem. For instance, 120 minutes of daily homework for seniors — the limit suggested here — is twice what most seniors do. In reality, it might not be so radical.

Tim Barnum, of Severna Park, suggested students who get A’s on exams should not be required to do homework. That violates long-standing educational practice. Maybe it’s time to experiment with new approaches, like telling teachers when homework is filling time but not teaching much.