Carla Ferris helps her 5-year-old daughter Mia Ferris-Artiga with her homework at their home in Washington on Oct. 16. (Kate Patterson/For The Washington Post)

Duke University psychologist Harris Cooper, the nation’s best-known expert on homework, summarized his most surprising finding 25 years ago: “For elementary students, no amount of homework — large or small — affects achievement.” There has been no significant challenge to that conclusion since. Nearly everyone in the national homework debate accepts it.

Cooper recommended a homework taste for the youngest children to “help them develop good study habits,” but no more than 15 minutes a day for grades 1 to 3.

So why does Arlington County, in my view one of the nation’s best-run school districts, recommend that the average third-grader get 45 minutes a day with another 20 minutes of reading four nights a week, much more than what Cooper and the National PTA advise?

An Arlington parent asked me to find out. The answer I got was in essence: simmer down.

“What we provide are guidelines not requirements,” said the statement from the Arlington school system’s Department of Instruction. It said the guidelines were the result “of careful and thoughtful work by parents, teachers, and administration and review and revision by the School Board.”

It quoted a statement from the National PTA that time limits might be a problem for children who need more minutes to finish their assignments. The department staff said “if a student is spending significantly more time than the guidelines suggest, then parents are encouraged to communicate that information to the teachers so that adjustments can be made and additional support, if needed, can be provided to the student.”

Many Arlington parents are over-burdened, impoverished and don’t speak the English language well. Relying on them to communicate with the teacher is risky at best. If research shows that homework in elementary school doesn’t enhance learning, why have rules for it at all? Cooper cites no data that study habits would suffer if children didn’t get homework until middle school. Something other than science explains why Arlington, like most districts in this region and in the country, cannot bear to say that it is okay to not assign homework.

I sympathize with the excellent Arlington teachers and administrators I have been watching for two decades. They serve a county with the highest percentage of college graduates in the country. Such a hotbed of academic success is going to be leery of dismissing the importance of assignments they did as children. The same goes for the other suburban districts in this very affluent, educated region.

But given the demonstrated talent of our local teachers, why not let them decide how much or how little homework is needed? Why not consider for elementary schools no homework at all, except reading? Arlington recommends a minimum of 20 minutes a night of reading for third-graders, but only as an addendum to the 45 minutes of homework. A few elementary schools in the area have had good results going with just reading.

That fits with what the Arlington Department of Instruction said: “Much of the homework that is assigned currently at the elementary level supports the focus on literacy.” The homework guidelines are maximums and so could be reduced to zero. Children and their parents could then just read anything they wanted.

The Arlington School Board policy says “the length of time spent on homework assignments should avoid undue intrusion on the time students may spend in other activities outside the school day.” The best way to ensure that is to forget guidelines for how much work should be done four nights a week.

I first thought that would be a tough sell. But I realized that a reading-only policy would allow the most ambitious parents to have their children go over spelling words or multiplication problems. Just how well their children would accept that routine would be a rich topic for future research.